I find a good way is to work with one or two good/quality dealers that you know wont b***shit you, it is possible... and listen to what they say in that how many copies they have had through their hands, i.e. if a dealer says its not rare cos he has had 5 ( or more ) copies through his hands over a period of time,then without being gullible its a fair comment. also taking into account that if one dealer has had that many there are other dealers with as good as if not better sources who MUST have had a few copies as well.
Unfortunately what Brian says is the most relevant and this is why prices are going crazy, nobody wants to sell them !!
guess we'll have to wait 20 to 25 years till we all start dropping off then there'll be a flood of records on the market and the prices will crash......I'm gonna take mine with me