Yeah, I know 7 ac is a lot of water. There are PTO driven pumps for some tractors that move a LOT of water, but it all depends on how much is coming in from the springs.
Have you tried keystone hatchery? They are just South of the Wi. border.
http://keystonehatcheries.com/largemouth-bass-0 All you need is LMB that are big enough to avoid predation from your other LMB in the pond. Say, 1/3 the length or slightly longer than the larger LMB in your pond now. You could stock smaller ones, but some will get eaten by the LMB in the pond now. 50 per acre would be a good starting point, depending on how many LMB per acre you think you have in there now.
