Here are some excellent sources of mosses for sale:

http://www.tnnursery.net/moss/

https://www.wholesalenurseryco.com/product-categor...

https://www.gardenplantsnursery.com/product-catego...

http://www.onlineplantnursery.com/sheet-moss/

http://www.tennesseewholesalenursery.com/moss-for-...

http://www.trees-plants.com/moss/

http://www.onlinenurseryco.com/live-moss/

http://www.gardendelightsnursery.com/mosses/