OK, I found you some. It will cost $50 + shipping.
j2-tech | eBay
Or you could thing big box store. Measure your tank, go down to your local big box store and think outside the box. What would fit over your tank? A small garbage can, a planter, a square tool box ... walk around with tape in hand.
Your typical office water cooler jug might fit if you cut the bottom off and slit it up one side. It is a little smaller in diameter but the "spring" in size difference might just hold it in place. The Krylon paints work great. One of my neighbours did their plastic patio chairs 3 years ago and they still look better than new.
Somebody must make one in black already look at the picture on the bottom of this page:
And you may want to look at this thread:
Single propane tank covers