tinted acne medications are available at any drugstore. you'll find them right next to Clearasill and Persagel.
but i honestly don't know how good they are. sorry!
MAC is available at selected department stores and stand-alone stores around the world, or through their website at:
there is a store finder on the site so that you can find the one closest to you.
since you're a student, i should warn you that it's a bit more expensive than other stuff, but a little pot of concealer lasts a year for me - and i have a LOT of broken capillaries and brown patches to hide on my face.
if you go to the MAC counter or store yourself it will be easier for them to match your skin *and* show you how to use the concealer to hide the zits!
whatever you do, DON'T let them pressure you into buying their brushes or sponges - you can get cheaper ones at an art supply store [or even Michaels Craft Store!] and cheaper sponges at the drugstore. buy a round one and cut it into 6 pieces like a pie - that's what i do!