I dont know what the name of the fitting is, but I made a couple of these for a friend a while back for his Caddy compressors. They worked pretty good till the compressors went tits up.
I had that Rancho setup years ago. The arms were about the same length as the stock lowers, but made out of rectangular tubing. The problem with the rancho arms is that they would hit the bottom of the shock mount during droop. I had to grind away the lower lip of the pad to get the extra...
www.columbiarubber.com
This is the company that does our vulcanized rubber idlers. Not sure if they will do one part or not, but worth a shot if you run out of options.