I've been recycling cartridges for a few years now. Summit Laser Products (formerly Chenesko Products) has comprehensive product and technical information.
Although they are not aimed at hobbyists and do-it-yourselfers their emphasis on service is refreshing. Currently their minimum order is $60 with about 6%discount above $250. They can probably point the private consumer to stores which do handle single-unit sales.
Another distributor for the pro is Oasis Imaging (1-800-322-8992, New Hampshire for regional office).
Here are a couple of places who used to handle small orders. I haven't been in touch with in years, though:
Steven Michlin's LaserLand (orders 800-60-TONER) in Michigan Computer Friends (orders 800-547-3303) in Oregon had "starter kits"
Finally, RECHARGER Magazine intended for the remanufacturing industry only. Each issue is full of products and companies.