Rank: Wiz
Rating: 82%, 369 votes
Still not enough information, but taking a stab at it, I'll assume you mean the pinion rod that goes between the focus knobs, and engages a gear rack on the focuser. There are locations where they can be purchased, and you would need to provide the OD and pitch (teeth per radian) to match.
Try:
http://www.pinionrod.com/ as a source.