Here in the UK, P6x7s (any vintage) are hard to find apart from ones from Japan on eBay - lenses are easier to find, especially 300mm and above (which seem to be less popular). Shorter lenses are more practical and generally make more sense, but are harder to find and expensive. P67ii's are very rare and expensive. The 105/2.4 goes for silly money compared to other lenses (especially considering it is the 'standard' lens). Lenses could be from anytime in the P6x7 history - they've been marked as Super Takumar 6x7, Super-Multi-Coated Takumar 6x7, SMC-Takumar 6x7 and SMC-Pentax 67 - they all fit all cameras but there may be differences between optical arrangements, materials and the like.
I bought mine from a dealer (by chance they had one in) and lucked into a few cheapish lenses on eBay (some with minor issues). It's important to remember these are very old cameras, most received hard use by professionals. Back-in-the-day were extremely expensive for amateurs to buy new (the number of 'hobby used' cameras is going to be very low). As mentioned, some of the accessories (or any missing parts) are very expensive to source on eBay - the metering prism knurled shutter dial ring (I had to replace mine), strap lugs (original P6x7 ones are expensive but Optech 'B' type lugs are supposed to fit). Body caps, lens rear caps and the correct lens hoods can be more expensive than you'd expect.
Things to watch: Make sure the metering works in both open-aperture (lens switch on Auto) and stop-down (lens switch on Man) modes (one of my meters only works stopped down), check the meter chain isn't broken. Frame spacing can be inconsistent - but they shouldn't overlap.
Precautions to take: You can change lenses with the prism in place, *BUT* if you remove the prism you have to remove the lens before refitting the prism (risk of breaking meter chain). When winding on - guide the wind-on lever back to the closed position rather than letting it snap back. Always use a strap - it's a big/heavy/smooth camera - it's easy for it to slip if you're not concentrating. Loading film is fiddly at first - sit down, take your time - if you only get nine frames, re-check you're loading. As 220 film is almost non-existent today - set the 120/220 selectors to 120 and then leave well alone.
Fantastic camera and lenses - don't be put off by comments on the web about shutter/mirror slap or claims that you can't handhold the camera. They wouldn't have been sought after by professionals for 40 years if they didn't deliver the goods.
John.