Today I downloaded a free auto routing with POI Thai map from this source:
http://garmin.openstreetmap.nl/you have to put in proper parameters - like 'Thailand' in country field - and it generates (or directs you to) files in a directory which you download. I chose the Mac format (PC and Linux) are other choices.
In a few minutes, using Garmin's Mac software (MapManager, MapInstall, and BaseCamp) I was transferring maps to my Garmin 276C GPS device.
I cannot vouch for anything on this map, its auto routing features, POI's, completeness or last update status. I've only looked at it a few minutes in simulator mode. For my area (Chiang Mai) its fairly detailed for all the little roads in the area (east side of CM).