Can I get a COVID extension stamp after my 30-day extension on a 60-day tourist visa in Thailand?

Whether you can or can't go directly to the 60 day covid extension rather than take the regular 30 day extension you would normally get is between you and the immigration office you deal with. SOME are making people take the 30 day extension and then when that runs down they let them get the covid extension BUT other offices will let you apply for the 60 day covid extension without taking the 30 day one first.

SO, while it's not a cop out answer, the real answer is ASK your immigration office when you're there applying for the extension ;)