Chances are, if you look in the yellow pages of your local phone book, you will find the listings of various crafters.  Any one of them might have a few whimsical birdhouses for sale.  You might also want to ask your local veterinarian if there is a customer that makes decorative birdhouses for a hobby.  Aside from this, department stores, farm stores, and gift shops may all have whimsical birdhouses for sale.