Looking at the wear on that PLA rifle, I'm thinking a battleworn Cerakote finish would be an interesting finish for these. I'd be interested to know what PLA regulars think of the gun - since some folks are in contact. Might have to get a CJ650 to strap the gun to.
OR...
You could just use the gun the way it was intended until it looks like that, or if you are a snowflake, you could just sprinkle talc on a glove and rub the rifle vigorously for 15 minutes and it will look "battleworn" - which is mall ninja for "not a safe queen"
None of those options will cot you a $400 paint job to make you look like you use your gear.