I bought mine from lowes. It's in the spray paint section.
I also painted mine empty as it was a new setup. The drawback to this is the fumes. You will want to do it in a well ventilated area or in the garage. I'm eventually going to do it to my old 20 gal
. That one is still running so I will most likely empty most of the water in it (enough for me to carry it) and take it to the garage. It did take an entire can to paint the back of my tank with multiple coats.
Seems like a lot to do but the result is worth it. And they are starting to have additional colors.