I think it would be next to impossible to identify all sizes of stamps from all countries, as they come in all shapes and sizes and I'm not aware of any special standards they must meet.
The best resource may be to look at the Showgard Stamp Mounts web page (at this link) which will help identify the best standardized mount size to be used depending on the exact measurement of the stamp(s) in question:
http://www.showgard.com/size_guides.cfm