I have a set of completed knees and a unfinished MB gauntlet kit for sale:
First up, the MB guantlet kit. Parts are vacuum-formed plastic, and resin for the detail bits, rocket, etc. You get what is in the pictures - you'll need to trim, sand, assemble, paint, etc. SOLD.
Second up, a pair of generic mando knee armor. These are finished for a custom, but you can easily re-paint. They are styrene and are reinforced with fiberglass resin from the inside, so they are quite sturdy. Knee darts are resin. SOLD!