Welcome aboard!
The rubber boots are readily available, we stock them here. The are held in place by a metal ring that drives into the deep recess in the airhorn of the factory Pontiac Ram Air carburetors. This deep recess is NOT present in any other airhorns, so there would not be any way to retain the lower part of the boot.
The accellerator pump also has a groove in the top of the shaft to accept the upper portion of the boot.
It is still possible to install the boot into any q-jet, but it will not be sealed off by the retainer in the airhorn, and still may allow water to get into the carburetor.
On a side note, quite a few airhorns will have a recess in the pump area, and it would appear that the retainer would fit, but they are not cut out deep enough so that it will stay in place. We are able to machine those out here, to accept the retainer, but are not able to cut out standard airhorns that do not have the recessed area.
Hope this helps some?.....Cliff