I suspect it's really not that difficult at all. If you go to a large pen show, and know what to look for you can see a lot of money changing hands on stuff that you wouldn't give $10 for. Collectors know what they want, and have feelers out all over with dealers and brokers all the time.
A few are probably moved at the larger pen shows like DC, LA, and Ohio. I suspect that more go to well-heeled collectors who are subscribed to various mailing lists, whether snail mail or email. I know I get notices from several dealers about special edition Pelikans; although nothing in this price range.
There are also several pen specific magazines out there. Th two major ones in this country are Pen World, and Pennant. The latter is published by Pen Collectors of America and requires you to join. Both are quite good and quite different. But If you are interested in collecting or in pens in general, bot are worth subscribing to.
The point of the digression into magazines was that that is where a lot of these high end pens, whether limited edition or not, are introduced.
Hope this was worth your time.
Bill