How can I check if specific file is inside StreamingAssets?

So I have this feature in my level editor where an user can write in name of the music file to play. The reason you write it in, instead of picking from a list is that I plan, in future, to add support for user-created tracks in addition to tracks already in the game, which will be done by additional data files.

Anyway, long story short, I don't want players having to write full name (with extension) so my plan is to loop through all supported music extensions, including tracker modules and then selecting and playing first appropriate one. So if there's music called "techno.ogg", user can just write "techno" in the music field and it will automatically know after few iterations that you meant "techno.ogg" (checking raw file name first just to be sure if you haven't already provided it with techno.ogg).

That part is easy. What's hard is how to check if specific file exists within StreamingAsses folder.