Once the CCS1 adapter finally becomes official in the US along with the retrofit, I imagine a lot of current Chademo adapter owners will be wanting to get rid of it in favour of the CCS1 adapter. So you might find a good source of them shortly
Speaking as one of those USA drivers, I have to agree. I suspect that the majority of Tesla CHAdeMO adapters in the USA were little used. Most were probably purchased to combat (ultimately unfounded) "range anxiety." CHAdeMO charging stations will continue to be used by older Nissan Leaf and Mitsubishi PHEV cars. But that use will gradually decline through attrition, I imagine. And most Tesla drivers desiring a backup DC on-the-road charging source (in lieu of Supercharging) will probably switch to CCS1, provided the adapter is affordable and Tesla maintains an ample stock of adapters and parts for CCS compatibility upgrades of the older cars. Meanwhile, the (hopefully soon-to-be superfluous) North American CHAdeMO adapters should work for cars with Tesla proprietary charging ports in Japan, South Korea, Taiwan, and anywhere TPC cars have been imported (like New Zealand).
Make friends with a North American Tesla driver today! Wool sweaters, tours of LotR sets, and tuataras make attractive Christmas gifts.