I am not sure why you would have trouble finding one for sale if you go to ebay. I have gotten 3 Fs off ebay. two years ago I got a very late 2.8F in the 295xxxx serial number series with the Xenotar lens and I loved it (still do) so much that I started tracking all the 295xxxx serial number 2.8Fs that came up on ebay. I was surprised to count 61 of them came up in 2 years!! And that is just the 295 serial number. There are far more that come up with older serial numbers. so I would say that with a little time spent on ebay and the willingness to pay for it you could find an F if you wanted. The last one I got was for a friend who has no internet connection. I found him a 2.8F Planar in mint minus condition for 850 USD. That was amazingly cheap and lucky to find from a seller who made a poorly done ad.
DPurdy