Brian,
T.A are the kings (queen's?) of giant chainrings, and Mr. Barry at Bicycle Specialties, here in Toronto, has a the largest selection of rings on earth, and probally everywhere else, including ones so big you'd need a 24inch bb height just to keep it from hitting the ground.
Grant, 52t, McLean
T.O. (Toronto, Ontario) your source for T.A. (and t&a), Canada