They use to sell the tint sprays at auto stores such as Repco. I used this many years back on my other car for parking lamps and indicators....ended up going back to clear parking lamps ;)
Tip: You need to spray the tint on VERY evenly. When the lamps are off, it looks fine....but once lit, if it's not even, you will see light and dark patches.
For the rear lamps, I took to a panel shop to spray properly. Many years later, still looks fine. Was just basically thinner with a touch of black.