I've been talking to a couple of wholesalers about this very same problem, Hopefully I can convince then to start producing a limited number of necks for sale which are slotted but no markers or frets installed.
So far the plan is for Ibanez style and Fender style neck heals since those seem to be the main ones I'm asked about but these will have paddle headstocks so you can cut your own design out, plus it eliminates trademark infrigment issues.
Some will be for locking nuts while others won't depending on the interest.
The first few of course will be rosewood fret boards as well.