Man I've been looking for eco friendly fabric on demand printers for years. It's tough.
Would be a great business model if someone had the desire and capital to go in.
Especially hemp the market should continue growing quite nicely, and hemp shirts are great and super comfy (I own a couple).
I've contacted the on demand printer apps in the Shopify store to ask / recommend hemp but haven't had any luck with implementation.
I don't have a solution, but I wish you luck! 🌲