Anyone tried
www.modelfings.co.uk? They don't sell screw kits specified for a particular car or model, but they do have a huge range of fixings and their Cap Screw Box kits look very tempting.
http://www.modelfixings.co.uk/cap_screw_boxed_kits.htm
Plus Modelfixings do all the odd sizes such as M2.5's. I've used RPC in the past and frustratingly they only sell M3/'standard' screws, so if your car has other diameter screws you will not get all the screws you need.