If you're desperate buy a 4 way plug board with USB sockets in it, readily available at Argos, B & Q and probably also Maplins. It will cost you a bit more than a standalone USB charger but as I said, if you're desperate...
Otherwise, CPC, Ebay and Uncle Tom Cobley and all.
EDIT: I see you've covered the plubboard angle - oops. Tightwad