Many local model stores will have a small range of Estes or Quest model rocket kits, and should sell suitable motors too. They should sell a starter kit, which contains a rocket, the launchpad and controller, but motors are probably separate.

For real enjoyment, however, it is definitely recommended to go along to a launch event of one of the UKRA affiliated clubs. Usually there is at least one model rocket vendor present, with a much larger and better range. There is no need to ask to be invited along, so just turn up and make yourself known at the registration desk.