I've been searching for the same thing. Unfortunately it seems like there aren't many people interested. Specifically because of the heat. I guess some people don't want to "melt"????
I found this group, but the person who organizes them is on "bed rest".
https://bkkryd.com
As for Bira Circuit, seems like there are track days, but doesn't seem to be many people attending. It would be nice if 20-30 people were there to make it a fun event.
Last time I was there a couple of weeks ago, I only saw 10 bikes.
https://bira.co.th/reserved/
I just picked up a new bike and am "dying" to get out to the track.