If you're thinking of Adelaide Fire Control - they have gone broke.
+1 for Ken and Steve from Ceasefire - very helpful guys. If you head down that way, they also appreciate a hand made beer being dropped off to stock up their fridge. Great service they provide, so consider them for your next refill.
Good info, I might see if they will fit mine as well (3kg bottle) otherwise I may get another bottle from Ken and Steve.I believe that you can get screw down valves for those bottles from
Boc Gas & Gear Mile End
291 South Road, Mile End, Mile End, SA 5031
p: (08) 8443 3519 f: (08) 8443 5602
For what it is worth, the thread on the fire extinguishers from Ken and Steve are 3/4 inch BSPF, and the screw down valves you need are 3/4 inch BSF tapered.