We searched high and low, all around Khao San Road for USD that would be accepted in Myanmar. We went to every bank we could find, every money changer, every hotel, everywhere. The criteria for the money is very particular: 2006 or newer bills, no folds, no creases and no stamps or writing on them. We would recommend obtaining the money before hand if you can, as we only found one place that had the required bills:
Au Thong Travels near Khao San Road. To get there, walk to the end of Khao San with MacDonald’s on your right hand side, to the gates where the police and parked cars usually are. Then turn right and walk past the Subway until you see an Ayudthya (yellow bank) across the street on your left. Turn right and head down the street opposite that bank. About 20 meters in on your right hand side is a hidden travel agent with the above mentioned name.
Make sure to check each and every bill as some of them are stamped by banks. They should have a few thousand dollars in the safe, but maybe go a day or so early to make sure they have the right amount you need.