The ORIGINAL PowerBooks? Like, the ones from 1991? Isn't it a bit late to be asking?
Regardless, airline adapters are widely available for every PowerBook and iBook model -- it's only the MagSafe-connected models that were left in the dust until Apple came out with this.
Targus and iGo both make universal (air/car/home) adapters that work on pre-MagSafe Macs. So do many, many other vendors. You should have no trouble finding one in retail or by mail.
tooki