That is actually a great place to keep looking. You will see a great deal pop up one day and be gone tomorrow. Check it regularly.
The other recommendation I have is Keh.com.
Keh is known amongst many photography buffs as being the best place to find great lenses, with great customer service and a great return policy. Their lens rating is super favorable as well, always towards the purchaser and not the seller (Keh).
Go take a look.
Finally, I would recommend forums based specifically with your gear brand. Go to their for sale/trade section and take a look at what is being offered. If you see something you like, make sure that member is a long standing one that many can vouch for.
One site I used to buy a lot of used gear from was Dpreview. They have a ton of people selling stuff. It is a lot more risky there though since there are so many people posting. It is more difficult to find well vetted sellers there.