Hi Camo.
The "Rustall" product is quite good. It comes in a four bottle set, "rust wash", clear, "dark wash", and a very very fine dust powder.
It runs around $18.00 USD and I've had good success in ordering it on line, i.e Squadron, Alpenflage hobbies, etc.
There are directions with the product that tells you how to apply it, and it really can be quite effective after some practise.
Good luck.
Steve