Had the same issue last year. The Amphur in bkk where we got married wanted a certified copy and my country does not have an embassy in Bangkok so that was impossible to do.
If anyone has any ideas around this please let me know. A lawyer wanted about 35-40k thb to help with this requirement and be a witness.
I didn't have time at the time to stay longer and explore other options but might go back next month and would love to do it without paying 40k for a lawyer :)