After a saga including an ignorant hobby shop owner (Maple engine mounts? What are those?), Sig being out of stock with the exact ones I needed (grr), I ended up with an acquaintance who owned a wood shop cutting down some large bearers from Sig to the size I needed.
He did a great job.
So if you know any wood workers who are willing to do the work and understand "meticulous", and if you (or they) can get the right sort of maple (there's more than one kind -- I think you want sugar maple, but you do want the hardest stuff available), then you can just have them made.