Well have fun with your kit! Building it is the most fun I think. For the 3 buttons I've seen guys use little circular magnets and just glue then on, if you went that route I'm sure you could pick them up at a home depot or lowes.
If you want just plastic buttons try contacting ATA, he usually parts out things.....never hurts to ask
Oh and btw.....SHOW US DEM PICS!