Hard to find, but when you find them, they are the greatest. Fresh supply in the Sansom Street Oyster House today at lunch--sweet, ample, satisfying, like being up in New England. Not bad for a $7.50 "appetizer" portion. That plus a half dozen pristine cherrystones @ $3.75 for a total blissed-out lunch quickie. If they are crowded, sit at the bar.