Yes of course there are nurseries also growing mosses, but number of sp. is rather limited.. And you get bags of dried tropical mosses to play with yourself i know i searched too.. 🙂
I got a terrarium shop a stonethrow away from my street, i sometimes go there for plants..
https://www.dutchrana.nl/en/
They also have a green house with all kinds of rare tropical orchids, ferns etc. etc. Also the most beautifull decorative mosses growing on the sphagnum they use to tie the plants on. i've asked, can i buy the mosses without the actual plant displayed. And the answer was simply no.. Also talked about it beeing a mis in the trade, there must be a huge market for it.. And he told me, i wasnt't the first to ask and not the first whit that idea, many have tried, but all failed to make even a bit lucrative all where limited to growing mosses everybody already is growing. There is nothing to compete with.. The mosses that come with the plants come on their own they don't do anything special for it.
He told he also tried in the past, then you have a nice batch growing and a week later everything dying and nobody can tell why.. Mosses are just too wimsy.. The only mosses he sells is Java moss and some liverworts.. Thats it. He has no supplier for anything else..