What bike are you lookin' for an airbox for?
I tend only to have genuine Ducati (Gia Co. Moto, MS Production, Ducati Performance, etc) parts.
I've seen some very good aftermarket parts, but they tend not to be of 'quite' the same quality (cheap, 'wet' lay up carbon, etc)
I also happen to have an airbox that'll be coming up for sale...