The 2 stores Zane mentioned are probably your best bet.
But if you want to do a little research before you call them, this site is usually pretty helpful with questions like this:
http://www.apple-history.com/
Find your computer on the timeline and it shows all the technical specs for that machine. This info is available many places, but I find this site easiest to search since it lets you list machine by category or by release date.