Thanks to all who replied. With your help, I located an adapter on Bulldog’s website:
http://www.bulldogtools.com/category370_387/product5527/product_info.html?osCsid=0ba41866943f3a9ad75dfddd72503226
Other suggestions for places to look mentioned were OWW, Fillauer/ Hosmer, Cascade, American, Endolite, and Ti-med.
Ossur adapter a145310 was suggested as well. It can be screwed onto a male pyramid which can in turn be threaded into a three prong. It allows the advantage of slight angular adjustments. The build height though with this set up is a little more than I need it to be considering the importance of knee center in cycling mechanics, especially a factor for knee disarticulations.
Zach Harvey
