I found this comparison of lens brokers over on the RedrockMicro site. Thought it would be good here so I copy it. Original post was by Nance McFarland whos's spelling I have corrected!

"I've been buying lenses for my adapter and thought I might share my research done in comparing the three main professional suppliers:-

Bhphotovideo.com
KEH.com
Lenses35.com

All three of these are well established companies with top rank reputation. Here are the pros and cons I have found in comparing them.

B&H: Large inventory but a bit pricey. Good for buying other video goods at the same time. Some of the more popular used lenses are priced close to retail. Take returns within 7 days.

KEH: Prices are average but grading can be suspect. I've had an EX+ from them that was no better than an E from lenses35 and their "like new" is just lenses35's E++.

LENSES35: Good prices and excellent return for any reason anytime policy. They are a specialist company selling lenses for adapters only so the inventory is limited. The good point is that you know that everything they have will work and is the best choice for adapters."

Cheers,
Indy