GMB would be my go-to place for 28mm Napoleonic flags, Maverick Models for pretty much anything else. The advantage of Maverick is that they'll let you scale the flag exactly the way you want. You order the flags, they e-mail you and ask for exact dimensions, you let them know and they print'em.
Recently I learned about Adolfo Ramos Flags, which seem to be very good: [url]http://flags.adolforamos.com/index.php[url]
Just out of curiosity - in what way are the Victrix flags 'too big' for your perrys figures? Too long for the white metal flagpoles the perrys supply with their figures?