You might try Ebay. I sold ours on there last summer, since we were moving to an apartment and 1) weren't going to have as much kitchen space and 2) thought it might be too loud and disturb the neighbors -- they are awesome but have a powerful/loud motor.

At the time I listed mine, there were a bunch of others for sale on there; some used, some new. In nearly all cases, the discount over buying directly from Vitamix was significant.

It's a great machine, just be prepared for the noise! We used to keep a pair of shop earmuffs in the kitchen for when we were using it.