hkparts dot net
Go to Adam Smith's site for HK parts. You will be able to find the sight adjustment tool there, as well as a plethora of other items you might want.
If not Adam, then Robert RTG parts has the port buffers for about $50 or so, which if you reload your ammo, is a must have accessory.
The V notch is a very hasty sight, for CQB. You just have to experiment with it, but generally, assuming it has been sighted in correctly with the 200 meter aperture and all works as it should, the front sight ring looks like it is sitting in the "bowl" of the rear sight notch. If you simply must hit something accurately inside 25 meters, you can center the front post in the little tiny notch in the rear sight, sort of like a pistol sight system.
But take it to the range and see how it works for you with different sight pictures.