I'm not sure this is the right category for this question, but here goes...

I saw a show where volunteers came up on stage and raced to see who could blow up a balloon faster by sitting on a pump. it went over great and everyone had a blast.
I asked the performer where he got the idea, he told me it's an old vaudeville game and there are a ton more like it. I've searched all over for similar games, but I haven't found any.
does anyone know a good source of these cool stuff?

I have not done research on this, so I don't really know where to look. However if you sat down with a pen and paper I'm sure you could come up with some in no time. Also you would come up with ones that are current and not 100 years old.

I've read a lot of the old trade newspapers (where they often published routines verbatim), and don't recall this, or a source for material like it. I'd love to know where he found it/them.

Talk to a Old Clown..these sound like the Classic old clown Gags like Bigger, Bigger,...Niagra Falls,..Atomic Hair-grower,...Tied Gag..ect. ect....

Yes, there are a ton of audience participation games. One is to do musical chairs by removing one chair at a time, but the rules are that everyone must fit on the remaining chairs when the music stops. It gets to be very funny as the people try to figure out ways for all to fit. Many party games can be adapted into stage routines.

I have several ooooold books of party games...time to look at them again!

I've sed a version of the balloon stuff with kids. Get em racing to blow it up. If one is winning grab the balloon and turn to the other one and say "hurry up, look how well se is doing ........" And let it down I the process.

To add a bit more to it or do it as a bar bet.........., use nappy wrapper liners (really long plastic bags with no end) ...... You can race anyone, give them a massive head start but still beat them use the phrase inflate rather than blow up. There is some physics in there if you don't know how to inflate it quickly pm me.