Myanmar is all about paper money now so there are no coins really in circulation. I would love to have coins from there but would be willing to bet you will have to buy them at inflated prices from hawkers selling to tourists. Hope to here an update from you after going there.
In Thailand it is easy to find coins. If you are lucky you will find some of the 10 baht coins commemoratives in change as long as your change amounts in the 10 baht range. The 25 and 50 satang coins are almost exclusively used in supermarkets so you will have to go there for those coins. The convenience stores do not use satang coins at all. They round up to the nearest baht. Good luck finding the 1 satang coins. My Thai friends have looked for two years for me and can't find anywhere that use them. If you discover the secret of finding 1 satang coins let us know. Keep your eyes open for the 500 baht Queen Sirikit commemorative note. I was lucky to snag one the last time I was in Bangkok.
There is a coin museum on Khaosan Road in Bangkok. If you have time, check it out. If you are into history go to the Rattanakosin Exhibition Hall near Wat Phra Kaew (Grand Palace). Hope you have a great trip there.
There is a whole bunch of commemorative 1 baht that I would like to have but I have no clue if one can find them in circulation or they would cost you an arm and a leg at numismatic place. If you run in to them and the price is reasonably low - I would greatly appreciate your help.
Для всього свій час, і година своя кожній справі під небом
