If you notice groups of well-heeled folks walking purposefully on the studio lots this week, they’re not tourists who’ve suddenly gotten a wardrobe makeover: They’re part of the 1300 foreign TV program buyers who’re in town to shop for primetime series which will launch over the next year.Their task is as tricky as that of U.S. network execs: They must identify the handful of American shows which might do well back in their homeland, beat the competition to them and try not to overpay for them. For the Hollywood studios, the trick is to convince the buyers that “Joey” will catch on the way “Friends” did, that “Savages” is just what the doctor ordered to get young males back to the tube, and that “Desperate Housewives” will help brand a station as hip. And it’s getting harder for the Hollywood distribs: Most foreign buyers are making their own shows or opting for cheaper reality fare. The studios nowadays are pulling out all the stops in efforts to place as many shows as possible overseas. If they can’t, they studios will have that much less money to reinvest in their dramas and sitcoms. If you bump into them, be nice to those buyers.