If you want bulk quantities, try a manufacturer.
Try Tufnol Composites in Birmingham.
http://www.tufnol.com/tufnol/default.asp?id=62
You want the 10G/40 Epoxy glass laminate and 2.5mm is one of their stock sizes, although they can make 2.4mm if you really want it. You will have to phone or email them to get prices.