A quick search of magnets turned up many sites, " http://www.unitednuclear.com/magnets.htm " and they dont look to expensive...

I bought some small "button" magnets at radio shack to hold down the canopy on my foam easy glider. I was going to use a screw on one side and a magnet on the other. The magnes were so weak I ended up epoxying a magnet into the fuse and another into the canopy so it was magnet to magnet. This worked well for this use but they wouldnt be strong enough for the prop balancer..

Steve