I have had a book for years - ANIMAL TRAPS AND TRAPPING -Don't know if it is still in print. It has a few ideas for homemade traps for various animals, but it mostly about the history of trapping. I will check the author and publisher for you when I get home.
I used to trap in VT, many years ago. Fur Fish and Game magazine used to have lorts of info on trap sets and supliers, had lots of ads.
Herters is still around. They used to sell a variety of traps.