I've never found a place the has the 7's in stock. I've always had to order them, but besides that no problems getting them. Do you have "Advance" near you, they can get them for less than $2 apiece. I'd figure any big auto parts place could order them.
Maybe you could order them online from carparts.com or something. I've only heard bad things about platinum plugs and have had bad experiences with them myself. I would keep trying to get the standard 7's. If you ever find them, maybe you should get like 5 sets . I'm going to buy a bunch next time I order some .