Curious about the issues you're having with rolling stock. Given Germany's industrial prowess, I would've thought that that wouldn't be an issue to manufacture, either for domestic use or export.
It’s difficult to just do a startup on general in this space (it’s sustainable mobility, but involves hardware, an old industry, old tech).
The state railways can afford rolling stock, but it’s extensive and takes a long time. They are not too innovative either, so may not solve the economics issues with new approaches, because they are too conservative.
As to finance, it does suck that we throw billions at economically, socially, and/or globally destructive, unprofitable startups and yet something that is a net good for society and environment can't get that funding. I guess that's where government steps in or private/public partnerships.
Good luck though!