Could even paint it OD Greed to match the JIC. But really, X is right, if you happen to have a hardware store near by (and who doesnt
), it's probably quicker, easier, and cheaper to make one your self.
You could even go a little further and get a strap setup for ease of carry. Good strapping is available from Outdoor sporting good stores, sold for backpacking. The posibilities are endless as to how you could customize it for your particular needs.
It probably wouldnt be too hard to right up a sealing system like the JIC's. It's just soft rubber with a bolt to tighten and a plate to spread the force on the rubber.