I usually get prefab sheetmetal components made by Gray Metal Products.
Here's what they gave me for dealers in your area:
RE Michel - Wilkes Barre 1-570-829-0383
RE Michel - Scranton 1-570-963-7880
Olympia Chimney 1-570-504-7152
Chapman Supply 1-570-586-1611
If they do not have the item readily available they know that they can order and have sipped direct.
Here's their catalog: http://www.graymetal.com/catalog/Gray%2 ... 7_2012.pdf
See pg 70.