Paul,
I have been finding them on Ebay, and so far that is about the only place, I have seen them go for as high as 150.00 bucks, but I bought mine for far less, I think the average pice is around 60-70 bucks. I see one on there about once a month.
They all appear to be in unissued condition, I have not seen one yet (either the two that I own or the ones on auction or on collector sites) that have the black paint or any other markings (unit, rack numbers, country marks, serial numbers) and the reason I mention this is because at an old military surplus store near my house the owner had some really nice unissued canadian marked WWII breech covers, when I asked where he got them from he said that he knows a guy in canada that found a warehouse out in the sticks that was falling in on itself and was full of military stuff. So I wonder, if the story is true, if these were not made, boxed away and then these are now coming from the same source.
Ryan