You can pick up an extra mag at pretty much any gun shop. I got an extra 10 rd mag at Gander Mtn...great to have when at the range. I've shot a few different kinds of ammo through mine, Federal Premium, Blazer Brass, Winchester, etc. Everything has been factory loads. I mostly shoot Winchester USA 115 grn fmj's. This is what I always have at the range and I have very good accuracy out of them. I carry Federal Premium HP Hydrashocks...too expensive to shoot many of them though.
As for the night sights, I'm sure there are many options available. I haven't replaced mine so I can't say I've done any research on them. However, if you like the option of a laser, check out the ones made by LaserMax that replace the guide rod. VERY NICE for semi-auto's.