This is the Umarex offering:
http://www.umarex.com/uxc.php?load=view&item=2.5733
It is 6mm and gas, as jassi says.
What I would like is 4.5mm and CO2 and a power rating of 3 joules not 1 joule (as above).
Unfortunately it is all a bit academic at the moment as the piggy bank is empty.