A complete kit for your TTR250 - all you need to add is the 20cc NOS bottle - available from the US.
I have not seen these kits sold in the UK but they seem common in the States but usually big car kits. There is one advertised for the TTR here which looks pretty much the same as I have for sale except the "2-stroke only" boost bottles aren't included.
£15 inc UK p&p anyone? A complete airbox cover that hasn't been hacked about is useful on its own