Spend some time looking thru

http://www.municion.org/

It's in Spanish so you'll need to turn the translator on to understand very much. It's pretty good overall.

This is also a good one. To find pistols or regular sizes ect look at the links on the bottom of the page.

http://members.shaw.ca/cstein0/metric.htm

http://members.shaw.ca/cstein0/riflelist1.htm