Parts are always on the electronic flea market and the occasional complete one does come up every once in a while, mostly from the US or Russia. I have also seen some authentic, complete ones for sale in Canada over the years at military antique stores here in Western Canada. I have not done active market research because I'm not looking for one so I can't say what the fair market value is, but the typical asking price of those that I have seen seems to be between $3-6,000. I understand that a post war MG3/MG42 tripod can be modified fairly easily to fit an MG34 if you're looking for something that's functional and economical but of little collector value.
There are a couple of fellow CGN members with adds looking to buy one on the EE, so you have some competition in that venue. However, they've been up for a while for whatever reason so I imagine it boils down to how badly you want one - There is an extremely limited supply available, but on the flip there is an extremely specific demographic looking for them. However, the supply is less than the demand and that's reflected in the price. I'm certain if you put up an add on the EE and advertised that you are willing to pay, say $8,000 CDN, word will get around quickly and you will get your mount. Otherwise, I would suggest attending militaria collector shows and making inquiries with dealers, calling established militaria stores or contacting some of the German re-enactor groups and asking them. Either than that, the easiest way is to get a hold of an MG3 mount and modify it to suit your needs (there's a YouTube video or two about how to modify one). Despite what Google led you to believe, there are more ethical dealers in Canada who have them for sale than the one you mentioned, so you have options in that regard should it be a concern.
Hope this helps.
Brookwood
EDIT - Are you looking for an authentic MG34 lafette mount or would an MG3 mount be sufficient?