I had a saved search running on ebay with my initials... 3 months later a G reg 5 character number plate came up, got for £150 as only bidder - transfer fees were already paid!
Ebay has the cheapest deals if you're prepared to wait for something. Ignore all the stupid expensive ones on there where if you push that letter against that, and stick a bolt in there it spells the word TWAT etc.