Grant makes a new one that fits w/o any adapter/drilling. I have it. It's a little larger than the OEM tuff, and the grip isn't as thick, but it looks and feels good for less than $100.00.
PGCLASSIC/BEA makes a leather one for more than 2x the above. I don't know the diamter though, but I'll probably pick it up too someday; just like the feel of leather more.