Normally, you would bind a weapon like this:
bind "c" "_impulse6"
However, I want to bind multiple weapons to a single bind. Something like this:
bind "c" "_impulse6, _impulse7"
So, when "c" is pushed, it switches to weapon "impulse6", if i do not have the "impulse6" weapon, it will go to "impulse7". I have done this in Half-Life/Counter-Strike using the above syntax. I'm pretty sure you are able to do it in Quake, just not quite sure about the syntax.
Multiple Weapon Bind Syntax
Look in the Binds, Commands, CVARs & Scripts thread, this is a known issue and any updates will probably be posted there:
http://www.quake3world.com/forum/viewtopic.php?t=11855
http://www.quake3world.com/forum/viewtopic.php?t=11855