Finding a File

Hello everyone -- I'm just a little bit stumped on this. I've got some files that are available for user download, however, the files are in different directories. The file names are based on the item number which is available. For example, item number "AS1000-01" is in directory "AS" and is named "AS1000-01.xxx" -- All files will have the same extension. That's no problem. Where I'm confused is not all of the directories are 2 letter names. For example, file "BSEB10-010" is in the "BSE" directory. Some directories are 4 characters long -- all except the BSEB**-*** files match their directory names until the file name contains a number (ASxxxx is in "AS", MASxxxx is in "MAS", etc). I need this script to be as dynamic as possible. I don't want to set up arrays of directory names or anything. Can I run through the string of item numbers until I hit a numeric character, and then check that substring to see if it's a directory? If it doesn't match exactly is there a way to search for that file in directories that almost match? Any ideas? Thanks, Joe