I'm just trying to sort out the same as my bike is stuck in East London. Here are the people I know of so far:
Bike Tyres On two Wheels
(This guy is now out of business. Just thought I'd mention in case you keep trying to call him).
Mobile Tyre Fitting and Puncture Repair
(This guy is very nice and will do central London. He did me a rear Dunlop GPR Alpha-10 on my old bike. He goes as far East as Sevenoaks but may do Canterbury if he isn't busy and you pay him enough!)
Domain Holding Page for Obantec.net Customer
(Not used this company and can't get through on the phone but they do within the M25 and other areas within "reasonable reach")
Sorry I can't be anymore help for the Canterbury side of things. Best Regards,
Ed