Nope, as far as I can remember not a single person can create more power armor.
The Enclave can. Even after FO 2 and FO3 they probably can, since we never saw the factories they use for PA production.
Arguably, the Midwestern Brotherhood can. Beyond those guys, you're right.
For example, who creates rubber (not condems) in 2280? Doesn't rubber come from Asia or something?
You can make synthetic rubber easily enough.