There's a process for reactivating all the unique traders, it's usually listed in their entry in the FO4 wiki. It sounds like you've already done some of it. Rylee is bugged above all others and has her own "fixes".
The key thing to remember before you get started is there are only a few repeating encounter areas where each show up, so you have to save scum and fast travel there (vanilla). Those encounter areas have a limited number of activations.
The Mechanist DLC ruins this by forcing it's random raiders into those areas as well. It's still possible to get most of the unique traders, but it's not easy.
There's more than one mod where you can use a terminal to "summon" most of the traders as well, etc. There's also a mod to change the Mechanist randoms.

He like the other rare random traders are exactly that: rare.

I've seen him in maybe 3 of my 9+ runs, and only ever recruited him once because I hadn't realized you COULD recruit him until only a few years ago.