Where Can I Find Companies To...

Jonathan, you have a lot of options (and I am sure you will hear from even more options on this forum :-)) You can use the service provider directory in the menu to the left. Go to the Vendors and Consulting link. Are you seeking a UK developer or somebody who can do the work anywhere in the world? In either case you might try one of the online project services, such as elance or rentacoder. (There may be some specific to the UK.)

If it's a major project involving multiple people, there are other options. If you provide a bit more detail, I and others here may be able to steer you better.

Good luck.

Matt