There are a few threads on travel forums asking where to buy US dollars with no definitive answer. I thought I would make a post to tell you:
- Where to get US currency (US$) in Chiang Rai
- Where to get US$ in Mae Sai
- Where to buy Myanmar currency (kyat) in Chiang Rai
- Where to buy kyat in Mae Sai
Firstly, you will not find US dollars at the Chiang Rai Central Plaza shopping mall. I learned this the hard way.
You can find US$ in Chiang Rai town centre at banks/money exchanges near the bus station. Some may just have a single bill to sell, some will have none at all. It seems there isn’t much demand for them to keep much. However, at Krungtahi Bank Currency Exchange on Thanon Phayonyothin (N: 19.90513, E: 099.83311) they told me they regularly have US$ available, and when i visited they had several hundred dollars in stock. The cashier me that often on Mondays and Fridays they do not have any, so it seems you are better visiting on other days if you can.
You will not be able to buy Myanmar kyat currency in Chiang Rai.
Getting US$ at Mai Sai is a little easier. I asked at the Siam Commercial Bank money exchange (close to the police station just before you get to the border) and was told that buying US currency was no problem at all. I said a friend was coming in to by a few hundred bucks in the next few days and the cashier said they would definitely have stock. It seems that Mae Sai has a higher demand for US dollars and therefore you have a greater chance of finding notes there.
Buying Myanmar kyat is also easy in Mai Sai. You cannot buy it at the banks/bank money exchanges. You need to walk back from the border crossing approximately 150m, until just past the police station. There you will find authorised money changers with all the Myanmar currency you need (N: 20.440240, E: 99.882002). Oh, and there are ATMs everywhere in Mae Sai, so you can withdraw Thai baht no problem.
Note also that at the border they require you to have at least TBH10,000 worth of currency before they let you across (THB20,000 for a family). However, I was not asked about this and i read elsewhere only very rarely will they check you have these funds.
Please also see my post on the border crossing from Mai Sai to Tachiliek here.