You can always do a search on amazon.com or the publisher's website to find the correct ISBN for each binding type. I also use fantasticfiction.com alot for this purpose and to find other books by authors I enjoy.

I agree, I would use Amazon.com for this, and go more off the original list price than whether it is calling it a paperback or a mass market paperback (7.99 and under is going to be MMP unless you get to fairly old books).

You can also look in the description of the book via any library catalog (best source is Library of Congress' Online Catalog) and check the dimensions.  The dimensions will be listed in centimeters on the same line as the number of pages.  Amazon also includes dimensions but uses inches rather than centimeters. 

Beware, though, as some libraries catalog all paperbacks, regardless of size, under one record.