Good news/ bad news/good news.
RE sourced their keys and steering locks from the same supplier as BMW. Key and lock shops will be of no help.
NfieldGear has tons (literally) of parts on hand that are not listed on the website. They should have the key blank you need and are nice people to deal with.
I forgot how to get the lock out of the steering head.
One of our forum brothers who knows old beemers will surely know.
Once the lock is out, any locksmith can fit the key blank to the lock.