There are Provari's in the classified section now in great condition from 100+. I have had great experiences in the classified section on the forum. Other than that you got fleabay, Provari's blem sales, or if you do Facebook some buy sell groups but the FB groups can be sketchy as there are a lot of scams out there.
If you are only going to save say 20 bucks from buying second hand versus the blem, you might be better off coughing up the extra Jackson to take advantage of being the original owner with Provape as I hear their customer service is really great and I am not sure how well that extends beyond the original owner.