This might come as a suprise to you but there is no one sitting on a stock pile of NOS, Open Box, or gently used units that we all go to when we want one.
Almost all of the ones I have seen in the last 20 years have been on Ebay or Craigs List or the like.
If you run across some one with a 20-30 of them in a collection your not likely to seperate them from them as hard core collectors fixated on one brand or one model are not usually in the market to sell their precious gems! When they die you will either see their stuff at an estate auction or on ebay or once purchased from an estate auction then on Ebay! If it has any value especially if it is listed on worth point you will see it on Ebay!
Be prepared to get into a bidding war!