I run the Bosch Plat +4 plugs as well!. Ive also run the single plats on every other car I own. (Guess I like em!)
I had copper top NGK's in there when I bought the car and as soon as I went to MSD wires and BP4 plugs there was a noticable difference. (Keep in mind my car may have just needed a tune up when I bought it)
Long story short, you can buy them anywhere! and they won't leave you hanging they are very reliable.
The Kryptonite! DON'T use ANY plat plug with a nitrous set up to my understanding the platnium plating flakes off and your in trouble.