Who is making Fx wildcat mag holders?

For info. I believe that there are 4 different mag holder locations for the Wildcat:
1. Inside the rear most gap on the stock. These are usually 3D printed, Max 3 mags.
2. In a 3D printed Butt plate extension max 2 mags. 
3. Individual mag holders slotted into the side of the scope rail. Either Alloy or 3D printed.
4. A picantinny rail which holds 3 mags horizontally 
Personally, I’ve found that with 3D printing, the quality varies. I would plump for either an Alloy side rail holder or the picantinny rail versions.