Yes, dog chews are sometimes antler. I put all my cut off pieces of reindeer, moose, and deer antler in a bin and take it to work for all the dog folks to take home. They love the big pieces. Even little dogs like to chew on a tine.
The best way to get whitetail ( or the local deer variety) antler is to ask some friends if they know someone who deer hunts. These people usually have plenty of antlers around, or will gladly save them for you.
All that said, the best antler for a knife is Sambar stag. European Roe and Red deer are also used. Sambar went up greatly in price over the past several years. Most knife supply companies still carry some, and Culpepper Supply is probably still the king of suppliers.
Final note:
Making a knife for yourself from a whitetail antler is fine, but most states have strict laws about selling deer and bear parts.