Well first off welcome to the forum. Next you need to narrow the geographic area down a bit on your question. What part of the country are you looking to hunt? What states cou;ld you realisticly be able to get to?
And take it from there.
What does "gauge" mean anyway? As used here gauge means the number of round lead balls the same diameter as the inside of the barrel (aka the bore) that it would take to weigh one pound. It takes 12 lead balls the same diameter as a 12 gauge barrel to weigh a pound. The smaller 20 gauge would require 20 balls of that barrel diameter. The larger bore 12 gauge would require 12 lead balls of the bore diameter to weigh one pound.
In general the number of pellets in a shotgun shell...