I need heat riser parts for my 250 cu chevvy six ('72 half-ton pickup).
The heat riser stuff is in the exhaust manifold directly under the section that joins the intake manifold. It is just above where the exhaust pipe connects to the exhaust manifold.

I'd check with NAPA, they should have it, if you can get a counter person to help. Also you can search their website by year, make of vehicle.