Is There A List Of Stamp Issuing Countries ?

When it comes to the 'nude women on stamps from South Arabia' type stamps, even the worldwide catalogs differ in their view on what are legitimate issues and what not. Michel and Y&T are generous in their listings: when approved by the proper authorities, issues are listed. Scott and SG are more restrictive: when not really postally used, SG moves an issue to the 'Appendix Issues' and Scott does not list the issue at all. Where you draw the line is up to you.

There are, aside from these (semi)legitimate but superfluous issues, really illegal issues. Stamps issued bearing the name of a country, not issued by that country. The best site on that type of issue I know is: http://www.pwmo.org/Illegals/frame-illegals-en.htm

Since you say you are a starting collector, my suggestion would be to select a catalog and take that as your guide. What is listed, is in scope and what is not, is out of scope. Stamps listed, that you don't want, you don't collect. A practical approach, that saves you a lot of time trying to figure out what is legit and what is not.

There are lots of legitimate postal issues that don't "fit" culturally with their issuing nations (winter sports stamps from Equatorial Guinea, anyone?). All that's necessary is a postal administration who wants to make money from selling stamps to collectors. If there's a potential buyer for something - nude paintings on stamps, for example, a seller somewhere will figure out how to sell it to them.