I put quite a few of mine on
Bikely in case anybody is interested in trying any of them out. There are many thousands of routes on there, but I couldn't find one for you.
However, I think I might have spotted one elsewhere. There is a charity ride in September which does London-Canterbury and judging from the comments of people who did the ride last year, it is the kind of route you are looking for. See
London to Canterbury Charity Ride.
I've managed to create a GPX file of the route and have uploaded that to Bikely for you -
here. It is the longer route that the charity ride takes. If you want to shorten it, just cut across from Shalmsford Street through St Augustine's along Chartham Downs.
You can download the gpx file using the Share menu option.
Have fun!