The experience market is essentially a subset of the travel market, and there aren't really "wholesale travel" suppliers. You have to go straight to the source to get the vouchers/tickets, or sign on as an affiliate/reseller with some of the companies who are already established in the field.
Experience Days (and their parent Extreme Element) are good ideas to approach; in fact, Extreme Element has a white label program available, if you're wanting to jump into that business with both feet. Incredible Adventures has an affiliate program, which is worth looking into given that they basically invented that business, and for the fact that some of their packages run into the hundreds of thousands of dollars (the cosmonaut training package is more than a quarter million US -- nice sale on which to get a commission, to say the least!)
If you have any actual venues local to you, it can't hurt to approach them about marketing, particularly if you have a unique or distinctive idea on how to present the experience, or ways to package it with ancillary/complementing services.