Checking some popular snaps on the snap store, I don't see any (in my very small sample size) besides snapcraft which are available for riscv64. And there's no way to filter by riscv64 like there is for other architectures.
It would sure be nice if there were a way to automatically build snaps for multiple architectures without each developer needing to own the hardware to do so. IIRC this is possible via launchpad.net, but not particularly intuitive. And many just build/publish snaps locally.
Anyway, perhaps a good first step would be to get @popey (and other prolific snappers) a RISC-V devboard ;) perhaps a new DC-ROMA II or Framework with RISC-V mainboard ??