I've never had much luck finding reverse log pots either. The obvious trick is to use a standard log pot but swap the two outer lugs over. You now have a reverse log taper, but you have to turn the knob anticlockwise to increase
Alternately, you can use a linear pot, which is a better match to a reverse log characteristic than a log pot.
Finally if you're really keen, you can get a 500k log dual gang pot in the mini Alpha style and dismantle it. The rear section is a reverse log, and you can swap it with the front one to get a 500k dual gang reverse log, or install it in the body of a single gang Alpha pot. I could never be bothered doing this though.