I know they can "reproduce" when, like you said, a bump forms and then falls off. Otherwise they can split apart naturally when they ram in to something, etc. If you want a carpet of tiny marimos you can purchase a few larger ones and tear them up. They won't be perfect balls for a while, but they look acceptable and will get better with time.
Thanks! My aim is to market to both aquarists and others, so we'll see how that works out. I think for a hobbyist, splitting marimos is a perfectly fine idea. However, I'm not sure that it makes sense as a business move- the larger marimos are significantly more expensive because it has been growing much longer, so splitting it up may or may not be a good idea at scale. I have found some very cheap pieces from larger marimo balls, so I may try rolling those in to balls at first.
If you do find any specific funds, I would love to hear about them. I know there are some Japanese communities that have local efforts and even festivals to conserve the wild marimo. I've attached a picture of a marimo bonsai, which I think is one of the coolest ways to use them in aquascapes.