Blue Arrow Train Sim (BATS) have now got a download library on their site which houses various things by them such as route updates, aswell as re-skins by other people. They have also just lauched a 30mb demoware Class 50 (50035 ark Royal) for free download including it's own cab and sounds! You do have to register (free) but it is worth it!
http://www.bluearrowts.com
http://www.bluearrowts.com