So far, I haven't come across any marked as such; not vegetable seeds, anyway, and I always check country of origin and packing date. But, the best way to eliminate it is cripplecreek's way - go heirloom. They haven't hybridized all the flavor out them, either.
"As democracy is perfected, the office represents, more and more closely, the inner soul of the people. We move toward a lofty ideal. On some great and glorious day the plain folks of the land will reach their hearts desire at last, and the White House will be adorned by a downright moron."
--H.L. Mencken, The Baltimore Evening Sun, July 26, 1920