I am going to retire in Thailand also ...
Answer to your question:
Non Thai residents (non citizens in Thailand) cannot legally own or posses a firearm)
http://www.thaivisa.com/forum/topic/169637-gun-laws-in-thailand/
If you cannot get into this URL Link you may have to join Thaivisa.com (just need an email address)...
Thanks. That pretty much guarantees I won’t be moving there. Can’t see moving to a country where, essentially, I’m the only one NOT allowed to own a gun! None of this affects my brother; he’s a liberal.