Is that still going on? In case you arent aware a whole lot of marimo moss balls got into circulation from Ukraine that where infected with zebra mussels. Zebra mussels are banned in the US (and probably some other countries) so marimo moss balls got taken off the market. I think there was a recommendation at the time in the US to completely tear down and clean out tanks that had moss balls in them bought after February 2021.
I think a lot of moss balls in the hobby are sourced from Ukraine anyway, so supply may on the low side because of the "special military operation". I know my LFS doesnt have any, but some other stores nearby do.
On a side note im thinking of making some marimo moss balls in a jar and selling them at a car boot sale. They sell online for £25ish and i recon i can make them for about £5 each. Try selling a few for £10 each to make a bit of pocket (beer) money.