there aren't that many frame shops that have employees. I think the closest thing to an apprenticeship I have seen is someone that has a friend that is a framebuilder and got them to teach them how to build a frame. The old apprenticeships were really just underpaid employees. Sweep the floor for a long time, then promoted to filing things, then much later cut some tubes, etc. It's a very slow process with a lot of unrewarding work. OTOH, you can learn in a school in 3 weeks. Problem is after you leave the school, you still have to amass the tools needed. My tool budget is small, and I wouldn't want a newbie to use the ones I have. Another complication is that most pro framebuiders have day jobs.