What area of the world do you live?
In USA and Canada roughly 50% or more of second hand switches should be exploitable. Consult web sites with serial number information about exploitable Switches and verify before purchase.
Ebay could work too but expect to pay a premium. Honestly better to do the leg work yourself and find a used one locally.
Keep in mind there are 10 million + exploitable switches world wide, so it's still fairly easy to locate one.