If you are prepared to go across the pond, it's listed at SJS sports cars in the UK (
http://www.sjsportscars.co.uk/index.php?mod=10) and no doubt Richard at Bank's Europa in the UK would have them on the shelf as well.
As you say I think the joint itself is a typical steering linkage joint, probably a bit more robust than the Triumph steering joints and more like one off a Land Rover or heavier vehicle. No doubt you could buy one of these joints and either weld or clamp it in place to the existing threaded sections from the old joint in the linkage, more work but easier to replace in the future.
As an aside, I replaced the rear joint by cannibalizing a new steering joint to remove the bearings & spider and then pressed them into place in the unique Lotus housings for the linkage shaft & gearbox rod. It's not difficult to do, very much like replacing a U/J in a propshaft, the old cups just pressed out and I seem to remember hacksawing the new one to minimise the damage to the bearings.
Brian
