I know Gitzo make a Monopod Holster,
Gitzo monopod holster, Series 1-5
Maybe the guys at VanBar might be able to get you one.
I bought a few years back a Lowepro AV kit, that had something that I have used to hold a small tripod, , It was a fold out Microphone pouch, fitted in my small slik tripod, also had a just a hoop like unit for headphones, that I could hang items on, they both had the Lowepro attaching system on them.
This is the only pic I can find at the mo, You see the mic in the pocket, and the loop at the other end. Don't think they are available anymore sorry.