In Bangkok, try the supermarket in Emporium (department store) - it has lots of imported foods and thus caters for foreigners. I think you'll get what you want there. Emporium Department Store is on Sukhumvit Rd. and has direct access to/from the BTS station. The supermarket is upstairs (4th. floor?????????)

Another place - the supermarket in Central Department store at Chitlom (again direct access from BTS station).

If not near either of these, I think any of the bigger supermarkets in the tourist zones would have all you want (e.g. Tops supermarket in Sukhumvit Soi 5, another in Silom Complex right by Saladaeng BTS)