Many thanks to SWLing Post contributor, Brian Penney, who writes:
I saw your post about the availability of the Perseus SDR. They are still available brand new through HRO. I ordered one in the fall of 2019.
HRO said they were getting them new from SSB-Electronic GmbH in Germany.
Thanks for the tip, Brian! The price is quite competitive at $749.95 US as well–certainly the best option for those of us living in the US.