Are you looking for a "twin", or "tandem" breaker? One with two handles in a single breaker?
You say you have one, yet you can't find one. I assume you need another?
What is the series? I'll bet it's QO. They are widely available if this is so.
Look on the breaker to see what series or model it is.
Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost.
Answers based on the 2008 & 2011 NEC.