There are a few companies that can help you out with pumps and diffusers. Being your pond is relatively shallow, you can also piece something together. My pond is deeper than yours but surface area is about the same (60×60 roughly). I purchased my system as a kit and it does a really good job. I wont say the companies name because they dont advertise on the site, but if you want their contact info just shoot me a PM.

.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!!