Personally, I only do maple leaf and american eagle in both gold and silver. They are highly sought after and have +value over spot price. Kitco and north west mint have always had best pricing. Locally, some seller asks for 10-20% over spot.. yikes!
https://online.kitco.com/
http://bullion.nwtmint.com/silver.php
PS.. how about producing some silver lower as ar-15.co collectible/fund raising.