There is unfortunately not a huge following for the Pro Jr., Blues Jr., and other off-shoot amps made by Fender, at least in regards to turret boards and other ready-made drop-in modifications. The big reason is that the amp is not as basic, simple, or easy to gut and rebuild as an Epiphone Valve Jr. for instance. The Pro Jr. is not a very complex circuit, but it is fixed bias, which adds circuitry and difficulty to its layout and parts needs.
Hoffman amps of EL34 World is the only place I know of that has a Pro Jr turret board and chassis-mounted tube build guide. They don't sell ready-made parts, they just provide the templates, BOM, and build guides. The circuit of the Pro Jr. is very similar to a Marshall 18 Watt model without the tremolo channel, with fixed bias instead of the 18 Watts cathode bias. Most builders are interested in the 18 Watt Marshall format. In general, amps that originated as a PCB build don't get much attention from the Builders and Boutique amp makers. The Builders are the ones who really drive the kit and amp modification market. The general fixes and mods for most amps are born out of demand for fixing only one or two things, and much of the limitation is due to the sensitivity and fragile nature of PCB amps. As a builder, I can't demand enough money to make changing out a single pot in a Pro Jr. viable and affordable to the end client. I am not a reseller, so I don't sell parts. I can build you an amazing Pro Jr. amp that will be built to last forever, but it will cost more than the Pro Jr. does from Fender. It will be free of the issues that bother EVERYONE, and it will sound as good as that circuit can sound.
What I can say is that while it looks daunting, working on the amp is an achievable task. As long as you are careful and do the best you can to only move it just enough to do the job, you can get the job done with little or no issues. Where you run into trouble is if you have to move the PCB board a lot, have to redo your work because you didn't do it right or you weren't prepared and have to improvise. The most delicate thing in those amps is the ribbon cables going to the tube's daughterboard. It is, unfortunately, easiest to work on these types of amps by completely removing all the PCBs together. This reduced the stress on the ribbon cables and makes doing the work you are in there for much easier to just do.
