You may want to buy the next set you come across. Apparently, UM was licensing this design from Craig Spegel and they had some sort of falling out and they're not making the grips anymore. That's why you don't see them on the UM website. There was a big fuss over on the Hi-Power board at 1911forum over this (apparently their Hi-Power grips were THE rubber grips). Shouldn't take much looking to find a pair, though.
You might also look at the Hogue Bantam grips.