I used GA3 to pop some recalcitrant land race seeds with success. It is available from Amazon. The concentration is important: 500 ppm, on seeds that are really difficult to germinate, 250 ppm on seeds that you think just need a boost to pop. Dissolve the powder in alcohol first then add to the right amount of water.
For really old and tough seeds you might want to scratch them up a bit first around the seam with fine grit.
Buena suerte,
-Grouchy