Dear Forum, Have a wood stove upland 207 prior 1984 cast iron, rear flue interior oval 8.5" x 5.25" 52,000 BTU, 2,500 SQ. FT. house with 8 ft. ceilings. Problem: need oval to 7" round coming out of rear in stove double wall black pipe. Can't find. any ideas or help could use. Thanks.