Gear Doc could get you Leimbach's bearing'd center pivot as well & Leimbach does have an endless spin kit to mate with it too.. but I hear it's quite pricey!
Other ppl make their own from scratch, including the endless spin for track drive power... have you looked RCP57's Volvo hoe build? That's a 98% scratchbuild that's near the same size as my Vario.. lots of innovation to be seen there.
http://www.rctruckandconstruction.co...ead.php?t=3135
I realize you're anxious to get going on making something now, but the constr forum is full of extraordinary ideas with many links to parts & pictures of how ppl did it for themselves... far too much info that I can't remember it all, but I know it's there. I guess it depends on what your ratio is of bought vs built it myself? I'm the "buy it now" builder so I get it working asap.
As for the hk hoe... there have been some who have noted that their model has worked perfectly from the day they 1st turned it on, and they have the later 1.5v version with the 4th valve to relieve the pressure in the hyd system when there is no valve movement.. perhaps their expectations of how it should work is much lower too. And there have been others too with the 1.5v that have commented their model has ran erractic.. it seems in my mind's eye that it's a crap shoot what you're gonna get, and being they are half the price of the others, ppl will keep taking that risk & deal with the problems as they arise.