You can from here read the Mahalakshmi Ashtakam (Ashatakam is a Stotra composed of 8 verses) which is of course dedicated to Goddess Mahalakshmi. The Stotram was said by Devaraja Indra and is found in the Padma Purana:
नमस्तेऽस्तु महामाये श्रीपीठे सुरपूजिते ।
महालक्ष्मि नमोऽस्तुते ॥१॥
Namastestu Mahaa-Maaye Shrii-Piitthe Sura-Puujite |
Shangkha-Cakra-Gadaa-Haste Mahaalakssmi Namostute ||1||
1.1: I Worshipfully Salute Devi Mahalakshmi, Who is the Mahamaya (the Primordial Cause of Creation); And Who is Worshipped in Sri Pitha (Her
Abode) by the Suras.
1.2: (I Worshipfully Salute Her) Who is adorned in Her Beautiful Form with Shankha (Conch), Chakra (Disc) and Gada (Mace) in Her Hands; I
Worshipfully Salute Devi Mahalakshmi.
But this clearly is the depiction of Sri Lakshmi and not that of the Supreme Goddess Sri Lalita Tripurasundari.
The next verse of the Stotra makes things even more clear:
नमस्ते गरुडारूढे कोलासुरभयंकरि ।
सर्वपापहरे देवि महालक्ष्मि
Namaste Garudda-[A]aruuddhe Kola-[A]asura-Bhayangkari |
Sarva-Paapa-Hare Devi Mahaalakssmi Namostute ||2||
2.1: I Worshipfully Salute Devi Mahalakshmi Who is mounted on the Garuda, and Who is the Terror to Kolasura,
2.2: (I Worshipfully Salute) the Devi Who Removes All Sins (when we Surrender to Her); I Worshipfully Salute Devi Mahalakshmi.
As regards, the supreme Goddess Lalita, then she does not ride the Garuda and we find from the Lalita Trishati of the Brahmanda Purana:
Lagna Chaamara Hastha Shri Sharada Parivijitha
Sharada (or Sarswati) serve you with Chaamara as a hand fan;
And, this is depicted in the following image of the supreme Goddess:
Also, it is a common practice to add Maha before a deity's name, it does not change the deity itself.
For example, this page describes a Ganesha Puja. But while invoking the deity the Mantra being used is Mahaganapatim Dhyami Avahayami
Similarly, this page describes a Vishnu Puja, but the invocation uses the Mantra Mahavishnum Dhyami Avahayami
Therefore, Lakshmi and Mahalakshmi both refer to the same deity. And Lalita is of course the supreme Goddess and is a different deity.
As requested by user SK.. updating the answer.
The following passage from the Devi Bhagavatam (DB) proves that the supreme Devi is the combined form of Mahalakshmi, Mahasaraswati and Mahakali. So, Mahalakshmi is immediately ruled out by this from being the supreme Goddess.
S’iva is beyond Prâkritic attributes, eternal and ever omnipresent;
She is without any change, immutable, unattainable but by yoga; She is
the refuge of the universe and Her nature is Turîya Chaitanya. Mahâ
Lakshmi is Her Sattvikî S’akti; Sarasvati is Her Râjasik S’akti and
Mahâ Kâlî is Her Tâmasik S’akti; these are all of feminine forms.
21-25. The assuming of bodies by these three S’aktis for the creation
of this universe is denominated as "Sarga" (creation) by the high
souled persona (Mahârpurusa), skilled in S’astras. And the further
resolution of these three S’aktis into Brahmâ, Visnu and Mahes'a for
the creation, preservation, and destruction of this universe is
denominated (in this Purâna) as Pratisarga (secondary ereation.
DB Book 1, Chapter 2.
The same can also be proved by using Sri Chandi (from the Markandeya Purana) as the reference.
Further references, that prove that Lakshmi and Mahalakshmi are not different deities and that she indeed is the consort of Lord Vishnu are given below:
20-22. Janamejaya said :-- “O Bhagavân! In olden times, the World
mother Parâ S’akti handed over Gaurî to Hara, Laksmî to Hari, and
Sarasvatî to Brahmâ, born of the lotus from the navel of Hari. Now I
hear that Gaurî is the daughter of Himâlayâ as well of Daksa; and Mahâ
Laksmî is the daughter of the Ksiroda ocean (ocean of milk). They were
all originated from the Prime Devî;
DB Book 7, Chapter 29.
This very beautiful Laksmi Devî is the complete master of the senses;
She is of a very peaceful temper, of good mood and all-auspicious. She
is free from greed, delusion, lust, anger, vanity and egoism. She is
devoted to Her husband and to Her Bhaktas; Her words are very sweet
and She is very dear to Her husband, indeed, the Life and Soul of Him.
This Devî is residing in all the grains and vegetables and so She is
the Source of Life of all the beings. She is residing in Vaikuntha as
Mahâ Laksmî, chaste and always in the service of Her husband. She is
the Heavenly Laksmî, residing in the Heavens and the royal Laksmî in
palaces and the Griha Laksmî in the several families of several
DB Book 9, Chapter 1.
Do you need more proofs? Anywways, why Lakshmi is called Mahalakshmi is given in the same Purana:
The two-armed person first made over to Mahâ Laksmî the four armed
One; then the two armed Person Himself took Râdhâ. Laksmî looks on the
whole universe with a cooling eye; hence She is named Laksmî and as
She is great, She is called Mahâ Laksmî. And for that reason the Lord
of Râdhâ is two-armed and the Lord of Laksmî is four-armed.
DB Book 9, Chapter 39
And, here the two-armed person being referred to is Narayana or Lord Vishnu.
1-2. Nârada said :-- “O Lord! How did the eternal Devî Mahâ Laksmî the
dweller in Vaikuntha, the beloved of Nârâyana, the Presiding Deity of
Vaikuntha, come down to the earth and how She, became the daughter of
the ocean? By whom was She first praised? Kindly describe all these in
detail to me and oblige.”
Book 9, Chapter 40.