I am assuming they have to be by the way they are already wired to fit the harness. They are the 520 series lights that use the 12v 85w H3 bulbs. Are there other brands that fit?
You will probably notice a difference. The PIAA are a good quality bulb and produce a whiter light than your average halogen bulb. But any H3 bulb will plug in and work from a Sylvania silver star (which I DO NOT recommend due to a lousy life span) to a regular auto parts store bulb to a PIAA bulb. Personally I'd go with another PIAA set but they are quite a bit more than regular bulbs. As for where to get them I'm not too sure. The last set I got was in Raleigh at a speed shop, but for the life of me I can't remember the name of it. Probably on line is your best bet.