Thanks! For my mom's tourist visa extension. (Always like to prepare everything ready beforehand )

http://www.immigration.go.th/nov2004/en/base.php?page=download

Try Don's Life in Thailand he has all the forms on his site plus a lot of other neat stuff

This may not apply to tourist visas, but for extending my non-immigrant B visa, Immigration refused the form I'd downloaded and printed on A4 paper. I had to use THEIR printed form on special paper, which was otherwise identical. I hope that's not the case with your mother's tourist visa. (Pointless offering forms for download if they're not acceptable if you ask me, but TIT.)

At the top of the form that I printed out the first time I tried was written 'Bangkok' in Thai, which I didn't recognise then. I also had to fill out a new form by hand, no trouble since though.