Did you try Google Earth with Roads enabled. Some parts are clear but other not yet.
Another alternative is Point Asia at Link removed I think you have to subscribe and the satellite pictures are pretty detailed if you zoom in but road names are in Thai as you can see here:
You would have to do quite a bit of copy/past to make this in a somewhat larger map. As an alternative, the 1:50000 maps from the army as Harry mentioned. These maps are quite good but old and do not have all the newer roads. In the near future, newer versions of this series will be available but don't know if these will be available to the general public (even now some of the older maps are still offlimit including the map for Sukhothai for some obscure reasons).
More or less the same are shown here from 5135 1 (7017 series) which shows that newer roads are missing:
and just, for comparisons sake, more or less the same part from Thinknet (at 1 :50000) and finally the ESRI GPS map: