If you need it, don't know. Two options, dental schools typically require volunteers for practice, they tend to charge a fee loosely designed to keep the in flow of patient test dummies where they need it, but invariably cheaper and entirely safe.

Additionally, the Mexico option is a real one, Mexico is neither a third world country nor absent trained dentists, many people do go that route so that there are actually a greater number of facilities on average near the border then elsewhere, I don't really advise that route but I'd suspect it is quite safe and obviously much cheaper, quality and risk are likely to be different then the US, but I doubt by too much, if your dentist can give a name or specific facility, it may be worth the risk as he's clearly looked into it, if not, then I'd definitely not go that route. And I'd definitely suggest the colleges first.