Guru mantras for people without a guru: Is there any scriptural support?

Question

The general consensus appears to be that a living guru who is accessible and can give initiation to the seeker is absolutely essential for any form of progress in Sadhanas.

However, in his book "The Ancient Science of Mantras: Wisdom of the Sages", Om Swami gives the following mantra for people without a human guru:

gururbrahmā gururviṣṇurgururdevo maheśvaraḥ, gurureva paraṃ brahma tasmai śrīgurave namaḥ.

This blog post claims that people without a guru can invoke Lord Shiva as a guru with the following mantra:

ॐ हंसः शिवः। सोऽहं हंसः। शिवः हंसः। शिवः सोऽहं।

On the same website, this other blog post offers the following guru Gayatri for people without a guru:

ॐ गुरुदेवाय विद्महे परमगुरवे छ धीमहि तन्नो पुरुषः प्रछोदयात्

Is there any scriptural basis for any of the above claims?

Answer 1

The first one is ordinary, it can be chanted and is taught to kids as well.

The second mantra that you have stated is not what the website claims to be. It is the Guru Paduka Mantra, given at the time of intiation itself. Rudryamal Tantra :

Along with the mantra given (the Mool mantra) , the Guru paduka mantra is also given in the Diksha. Only After performing the japa of Guru paduka mantra, the japa of IshtaMantra commences. This mantra appers as 'Laghu' (short) and 'Purna' (complete). Also the mantra involves the Remembering of ( by involving Diksha Nama) Name of Guru, the Param Guru and Paramesht Guru as well as their 'Shaktis'. which is conducted in the Sahashara Chakra using the Mrugi Mudra. By performing the Guru-smaran this way, the mantras give immediate results.

As stated this mantra is 'Guru-Paduka-Mantra' and not a alternative for people without guru to invoke shiva as their Guru. There is even the Maha Paduka mantra and even the Ucchishta Maha paduka mantra given by guru only which make the person eligible in his sadhana.

The one stated here: (seems it's even stated wrongly, or may be I havent come across it)

ॐ हंसः शिवः। सोऽहं हंसः। शिवः हंसः। शिवः सोऽहं।

The one stated in Rudrayamal:

ॐ हंस: शिवः सोहं सोहं हंसः शिव: हंसः शिवः सोहं हंसः हस्ख्फ्रें हसक्षमलवरयूं नमः ॥॥

See this for instance. I am unsure about third, someone will answer about it.