Rob,
Can't help you with that one i'm affraid, however an alterative is the kit by Winspray. I use their belt sysyem and it is good stuff and very comfortable to wear.
They do a holster for a small drinks bottle which includes the bottle, simply take the top off that bottle and substitute it for a spray head ( The thread is the same ) It works a treat. Winspray kit is available from the Window Clean Centre and Wintecs.
Denzle