If there is a cad design then sending it to companies like pcb-way might be a option
If resin printed part are fuel-proof then that would be the easiest/ cheapest way or else have it laser sintered from metal powder like space-x does for there engines.

Once proven it more becomes a issue of building a digital libary of designs and then have a company lik pcb-way make it once there is a order for a particulair design.