I used to use https://www.martialartssupermarkets.com but I had a few negative experiences with them. About two years ago, I discovered https://www.karatekorner.com by accident. Their prices are very competitive and their service was excellent as well. My $0.02
IMHO, stretchers are only good if you use them on a continued basis. Like any type of exercise equipment, machines tend to bought, used for a little bit and then thrown in the closet.
I prefer ProForce gear myself. It's inexpensive and fairly durable. When it wears out, its cheap enough to replace. KarateKorner.com is where I've bought mine in the past.