What's wrong with the Mamiya Tareq? Just to make sure you know, they will not test fire with the back closed or the shutter blind closed (the dark cloth shutter in the rear that allows you to change lenses without fogging the film). In order to test fire, you need the camera back open. It will also not fire if there is a little red light lit in the lower left corner.
If that does not solve the problem, I would try cleaning the contacts on both the lens and the camera body. Even if you bought them new, these have probably been sitting on the shelf for a long time, so there might be some oxidation...you can try cleaning it with some sort of rubbing alcohol or other cleaning fluid. Also, make sure to check the really simple stuff, like having the right batteries and having them inserted properly. I think most of these Mamiyas are pretty well made and there is generally not so much to make them go wrong since they are pretty simple electrically.
As for the Cezanne and drum scanners, be very careful about buying them...most are very old by now and need a dedicated computer to run them. Many cannot be easily serviced anymore and the drum scanners in particular require a lot of effort to use. If you want a scanner for personal use, it is generally much better to use a dedicated film scanner like the ones from Nikon, Minolta, Epson or Hasselblad/Imacon. Then if you still feel you need a drum scan, you can send it out to someone else to deal with. In terms of where people get them, I would assume most get them from eBay, labs and printing studios that are closing or no longer need them, or from one of the clearing houses that service these industries (Genesis Equipment Marketing, Footprints Equipment, etc).
