Those chains on ebay plus the ones sold by XRsonly are the only new chains I know about. I bought mine from XRsonly back when I was rebuilding my two engines.
Funny, the ebay listing for the PROX has the wrong part number in the photo, but the description states the right number.
If you were interested in this brand then I'd send them a message through ebay and make sure about the part number they are selling.
The only other option I could think of for finding decent chains is to do the parts search on those other bikes that supposedly have the same timing chain. I'll eventually need another chain for a third engine build I'm planning but I'm not in a hurry to spend money right now either
Other bikes with same chain as listed on the cheap ebay chain listing:
LT300EH/EJ/EK Quadrunner (1987-1989)
XV500K Virago (1983)
XV535 Virago (1987-1997)
XV650 V-Star, All (1998-2005)