Well the Blaze is fun of course and this is really a minor issue. Superspars and Cirrus use stainless or equivalent in all high stress places so why not keep it simple and just get hold of a few. I've never seen stainless ones fail on any Blaze goosneck well ..... er ever ! 'DIY store' rivets are about as useful as using chewing gum on a racing dinghy.
Even good quality alloy ones should be fine and the gooseneck should not come under too much load anyway unless the boom is slamming into the shrouds (tie a strategically positioned knot in the mainshet to stop that!).
Anyway come to the show buy a small handfull of s/s rivets, and simply have fun ! Keep us in the picture as to what works in the end for you.
Cheers - Mike Lyons
PS - there is a life after Lasers ...(and if you are old enough there was plenty before as well !)