The Pentax 6x7 is a giant version of the typical 35mm SLR. It was designed that way.
The Mamiya 6/7 is also similar though it is a rangefinder camera ... I like these better than the Pentax.
The more typical medium format camera's took the shape of a box ... the Hasselblads are the most common of that type.
I had the Bronica SQ-A ... I preferred the square 6x6 over 6x7.
I found that the Blad physical form was better to handle than the SLR form for MF.
There are plenty of MF camera's on the used market as many have gone away from it to Digital.
The question of where to get these cameras, in Canada ... well Henrys used to be a good place but they also have gone away from film, though I have not been to the downtown store in decades ... go to the PHSC fair as Blacksheep mentioned.
If you want to get 6x7 ... there is the Bronica GS-1 or Mamiya RB/RZ67
I have ended up ordering film from Henrys and also
B&H (USA).
FYI: there is a Medium Format forum here:
http://www.thephotoforum.com/forum/medium-format-large-format/