I’ve welded, was pretty good at it, and being a plumber just mastered soldering pipes, idk what to do as for a seat, find one or make one? In time..As you never welded, it looks almost impossible to learn. But even after 20 years not welding, I am building my frame. My welds look terrible, but I clean them and the frame holds me.
Brad made great instructions on how to put the frame togheter with tips and tricks.
It made the build a lit easier and I changed the design.
You can look for companies near you, that work with steel.
I did the same and they cut the steel for me and made dome parts for me.
I could let them Madd the frame completely, but I decided to weld it my self and only let them cut a few things.
But maybe there is a company near you, that can help you if needed.
I decided to do most by myself to save money and use it as a learning experience.
And I am happy that I decided to make it myself. After this project, I will start with a project for a shop, but also on my next project.
If possible, try to build it yourself. Else I would try to look for a factory near you, that maybe can help you.
As you want to let it be made by a factory, than you need work drawings. Many factories prefer work drawings and will not cut a bike in parts to use it.
As you lived near me, then I would have build a bike with you.
One tip, check how you want to sit on the trike. I raised my seat a bit and didn't go for the low angle what I first wanted. Getting out wasn't that easy and still is harder than getting of a normal chair, but a lit better than I planned for first.
Low is great, but as you can't get on and off the trike, then you won't ride a lot.