Another thing you should do before replacing "worn out" blades is to clean them with an alcohol wipe. This should remove the buildup of fine gunk away from the sharp edge of the rubber. It's that sharp edge that does the cleaning.
Yeah, the front blades were honestly fine (could have been cleaned) but the rubber on the rear one got ripped off by some ice so I figure if I'm replacing one, might as well replace them all.
Yeah, it takes some searching, but some auto parts stores stock just the blades themselves, not the entire arm. 'Lots cheaper and seems to work on my cars.