I checked around, and Spinda has exactly 2^32 variations, or 4,294,967,296. You have a 1/8192 chance of having a shiny pokemon, so the probability of having just two is:
1/2^321/8192=3.518 E13=chance of 1
so the chance of having two is
-assuming my math is correct, you have a 1 in 288230376200000000 chance. Good luck with that.
It's about a .0000000000000001% chance by the way.