Is the re-entry permit still available to buy at Suvarnabhumi Airport for expats on a non-B visa extension?

follow the signage

The last time I used it , it was well sign posted . It's at security gate 2

I do not know where you heard those rumors. The re-entry permit counter is still open at Bangkok International Airport at Terminal 2. When you are at passport control, let the passport control officer know that you are getting a re-entry permit, and they will point to you the counter. The desk may not be manned, but they can get someone to issue the permits.

The cost is 1K THB if you fill out the paperwork, or 1,200 THB if you let them do it.

You can also get a re-entry permit at any immigration office. For Bangkok, you would use Counter C-2 at Changwattana.