Which places in India does the authentic “pitru vidhi” happen?
IMO, while this question can't have answers from the scriptures but the following can have:
Which is the best place for doing pitru related works (like pinda
The best is without doubt Gaya however there are many other places which are considered sacred pitru sthalas.
All the departed Manes, afraid of hell, seek it, thinking, ' The son
who will go to Gaya would be our rescuer.' (20) One should desire for
many sons, for if one happens to go to Gaya", or one happens perform'
a Horse-Sacrifice, or to dedicate a Neela Bull.
The deceased, for whom a bull is let loose on the' eleventh day, is
released from the region of the dead, and goes to that of the Pitris.
Many sons should be sought for, because one of them at least may
happen to go to Gaya, or celebrate a horse sacrifice, or dedicate a
Neela bull. (10)
Vrihaspati Smriti, Chapter 1 verses
Similarly from the Likhita Smriti's chapter 1:
If one, after entering Beneras, leaves that place on any occasion and
goes elsewhere, the Bhutas (spirits) laugh, striking their palms,
The person naming whom one offers a pinda at
Gaya, goes to the celestial region, if stationed in a hell ; and
attains to emancipation, if residing in the celestial region. (12)
One takes him, whether he be his own relative or an out-sider, to the
eternal region of Brahman, by naming whom he offers a pinda at any
place in the sacred shrine of Gaya. (13')
Another verse from Katyayana Smriti's chapter 29:
Some learned men speak of the superiority of the offering of Pindas,
for, it is seen that, at holy places chiefly at Gaya, merely Pindas
are offered. (9)
Greatness of Gaya Tirtha from Kurma PurAna:
Gayaa Tirtham param guhyam Pitrunaam chaativallabham,
Krutwaa pinda pradaanam tu na bhuyovjaayatey narah
Sakrud Gayaabhigamanam krutwaa pidam dadaati yah,
Taaritam tarastena yaasyanti Paramaa Gatim
Gaya Kshetra is one of the most beloved Tirthaas of Pitru Devataas and
human beings who offer Pindas to Pitras have no rebirth. Even if once
the sacred deed of ‘Pinda Pradana’ is executed at Gaya, Pitraas would
be freed from Narakaas and are forwarded to Parama Gati. At Gaya the
most hallowed signs of Rudra Deva’s feet are imprinted on a Stone and
offering Pindaas there would most certainly bless the Karta and redeem
the Pitraas. Even while a person is in a position to visit Gaya and
perform the Pinda Pradana, he is lazy or careless and the Pitras
would feel disgruntled and dissatisfied. The Pitraas would vow:
Yadi syaat paatakopetah swaadharmarati varjitah,
Gayaam yaasyati yah kaschit sosmaan santaarayishyati.
Even if a person in my Vamshaa were highly sinful for any reason and
did not observe ‘Swadharama’ but had visited Gaya Tirtha and gave away
Pinda Pradana, he would still be liberated!
The PDF Essence of Knowledge of Numbers hosted by the Kamakoti.org gives few names of holy Pitru Kshetras apart from Gaya:
Yatra Shraddhas: are specifically related to visits of Punya Tirtha Kshestras like Gaya sheersha, Akshaya Vata, Brahma Kapaala,
Gangaasaagara Sangama Kushaavarta, Bilva, Neela Parvata, Prayaga,
Kubjaagra, Bhrugutunga, Kedara, Mahaalaya, Amarakataka Narmada,
Yamuna, Ganga, 85 Ganga dwara, Lalika, Sugandha, Shakambari, Phalguni
Tirtha, Maha Ganga, Tantu vikaashrama, Kumara dharva prabhava,
Saraswati, Kuru Kshetra, Naimishaaranya, Varanaasi, Agastya Ahrama,
Kanvaashrama, Pushkarini, Gokarna, Narmada, Godavari, Krishna, Kaveri,
Gomati,Vetravati, Vipasha, Vitasti, Shatadu, Chandrabhaaga, Iravati,
Kaanchi, Pancha nadi teera, Kaushaki, Saryu, Shona, Jyoti ratha,
Uttara Manasa, Badaba, Saoptarcha, Vishnu Paada, Swarga maga pradesha,