Maybe from another bent up one but they really only sell the springs and the nylon buttons individually. I feel you'll search for a year and not find just one half while you can find a real Comet driven in a few hours, tops.
WAIT! Before you buy, I was browsing MFG Supply and realized I was horribly wrong. You can buy individual parts here. You have to find whether you need a 6" or 7" face and whether you have a 5/8" or 3/4" jackshaft.