Linda, I ordered mine from a store on ebay - unmounted rubber stamps, personalized rubber stamps items in loongchai74 store on eBay!
They are reasonably priced. Not the best stamps, but they serve my purpose well and because they are economical, I could purchase 2-3 different ones, so that's what I did.
I'm not sure, but I thought Stampin' UP also had a stamp that you can customize. Is that true?