I got my latest (after a couple of others) from Tractor Supply. They are made for dealing with harness leather and are very robust compared to crafts level that you would get from Hobby Lobby and such. Just about any farm supply should have them.
I use and recommend this model from hobby lobby. It is forged and machined not stamped and bent. It is expensive how ever you can get a 40% off coupon on their web site to use in store or online. The punch tips are replaceable and this thing is dang tough. Any questions let me know and I will answer the best I can.