You probably wont find many adult BG for sale until after the breeding season this fall. You may be able to trap some out of another location and bucket stock them tho.
Trapping works well on smaller GSF. I'd leave those 3" fish in the pond. A 10" bass can easily eat them. Remove anything bigger. I seldom catch larger GSF in my traps, tho. You may just have to keep fishing them out. Dry dog food in a plastic bottle works well.
The females only spawn once a season so their numbers should be easy to control once you've removed the bigger fish.
.10 surface acre pond, 10.5 foot deep. SW LA. The epitome of a mutt pond. BG, LMB, GSF, RES, BH, Warmouth, Longear Sunfish, Gambusia,Mud Minnows, Crappie, and now shiners!!...I subscribe!!