I agree with the more instant gratification aspect. Ebay still is a place for astounding deals, you just have to luck out. Look at the completeted listings:
Shorthead: $900 BIN. Item #200129791089
Short combo with case: $1000 BIN. Item #330147185547
Shorthead: $1000 BIN. Item #130133432088
Wide combo: $1000. Item #130129649777
Although those are just a fraction of the Mark IVs that have sold on ebay, they still ended at very reasonable values. If you are just trying to steal a Mark IV for pretty much nothing, I doubt it is going to happen unless you luck out and someone has a low BIN or if the market gets flooded and bottoms out. I am not trying to come off like a dick, but the current market is not the best for a buyer right now. It just goes to show the Mark IVs are a very desirable amp and retain a good value.
All I can say is get a bunch of those Ebay auto search things for all the different names the Mark IV could go by: Mark IV, MK IV, Mark 4, MK 4, Mesa Mark, Mesa 4, Mesa IV. Sure they might flood your inbox, but you can come across a steal and luck out. I wish you the best with finding one. They are great amps and can tackle most forms of music. Just be patient and keep the lookout everywhere: Ebay, Craigslist, Backpage, The Gear Page, Harmony-Central, etc. You will get one, just stick with it!