heres another thing,
http://www.a5builder.com/
not quite the selection but its pretty cool. this site is mostly for paintball, the builder is (so dont click anything saying info or somethin cuz there all paintball parts) anyway, they have some airsoft stuff. the site is
www.opsgear.com
o and heres another. agian, not as big as selection.
http://www.arcoefrecce.it/softair/personalise.asp