Ok, my bad in misunderstanding your intent. To clarify then, you want to do work in your own shop producing something useful to a "client" at little or no cost to them? No training.
If so, then a simple marketing campaign is needed. It would have the same dynamics as starting a business. There will be considerable delay before a client base can be established and I can imagine that such a base would be sparse by definition. If for example one were to go door to door in a dense neighborhood looking for machining or fabrication work, one might not find any. People just don't think that way today. The work you offer is related to repair or custom work and our economy is "disposable" and mass produced. Few people fix things or buy custom. Specialized hobbyists sometimes need custom machining or fabrication, but again, they would be hard to locate and work would be scarce when one did find them. Commercial clients, perhaps overload work for a busy shop, don't fit your vision because of time and volume constraints. So it seems to me that your potential is quite limited, verified by the lack of success you have experienced in promoting it. Perhaps it takes a LOT of time. And patience. Some of the ideas mentioned I thought were pretty neat, but I'm not you, though we are in similar positions. Perhaps an extended definition of "helpful" would clarify a plan.
FYI, I have found that sharing my experience with an "apprentice" for a brief period of time is
most rewarding. Taking 60 years of woodworking experience, for example, and condensing it into a six week period showing a 58 year old lady, retired Navy vet, with no woodworking experience how to build a toy box/blanket chest with some sophisticated features using primarily hand tools and no rulers was both challenging and supremely rewarding. She covered the expense of materials, and in the process we became good friends. She came to me because she saw my web page, which no longer exists.
Here's an afterthought, again based on my experience. I got involved with a mechanical music hobbyist who needed a LOT of custom woodworking done. At the same time I noticed the very crude mechanical devices he "engineered". If you can develop relationships with the builders of these devices, and there are a LOT of them in the U.S., then perhaps you can realize your goal. Had we met 30 years later, I would have a rather fully equipped machine shop to address his Rube Goldberg efforts. Another area of experience is to find woodworkers who collect tools and refurbish them. They often encounter a need for custom made
replacement parts. e.g.
DanK