Ditto feed stores or farm fertilizer suppliers. As to how much to apply, I'd get a pH test kit and keep adding/mixing it in until the pH was mid to high 10 to low 11 range. You could drain water out of the pond by using a sump pump and concentrate fish in a smaller area, that way you have to use less hydrated lime.
Let me toss up a link here. Read it, do the jat test that they describe in it and go to google planimeter to calculate the surface area of your pond. Then do some depth readings to get a good idea of how much water volume you have. That, along with the jar tests will tell you how much Alum and Hydrated lime you need to use to clear up your pond.
http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=124005#Post124005 Use the hydrated lime to kill the fish, use the alum to clear up your water. It might be easiest to do both, (not just kill the fish) and if the pond is that small, you could do everything from shore.
