Thanks 53333, but like I mentioned to Longy above, it's not a tiller arm I'm looking for, but rather the coupling to attach the AP Drive and Rudder reference to on the quadrant. Thankfully Quattro is hooking me up with a replacement! To keep anyone else from being confused by my less than stellar description, here's a similar, though somewhat less complex, part for another brand. Ours is longer with two different shaft sizes and two cotter pins:
I think you are looking for the Edson tiller arm extension. I just bought one from Edson Marine for ~ $500. Easy install but you have to provide Edson with the bore of the rudder post to within .003 of an inch - easy to do with a good caliper for that size. FYI - Edson charges extra for oversize rudder post - it cost me another $150 or so for the machining. Turn time is around 4-5 days from submitting the order. You will need to get and fill out the "Autopilot Tiller Arm Data Sheet" from the Edson web site to show the bore size, location of the rudder post key and a few other items so Edson can make one that fits exactly.