If you can buy it in a store, just go through the pile holding each up in front of a brigh light until you find sheets that don't have the crud in them. If that is not an option, call the dealer and have them send a few sheets from a batch that they will be able to find again. If they look good, buy the whole package.
Alternatively, pay a premium and buy COT320 from Bergger or B&S. It is basically the same paper, but I think that Bergger must have more stringent quality requirements, because I have found that I have much less problem with the black spots. In all other respects, it is the same paper and I treat it exactly the same.
As far as what I do with the speckly sheets - It is a bit of a crap shoot. Sometimes, a few small specks won't cause problems. If I can orient the negative so a potential problem speck is in a deep shadowed area, I'll go ahead and give it a shot. If it is riddled with junk, it makes dandy backing for vellum prints or covers for prints in mats.....
Or switch to Whatman's. And yes Jorge, I still owe you some. I'll try to get my lazy texas butt in gear and get it out this week.