Seals for gas boiler exhaust pipes

[ss]

Where can I get a supplier for the above (online ordering) It is the pipes that come of of the top of the boiler that I believe is the air intake and the exhaust (inner pipe). It is the seals that connect the lengths.joints of the pipes. Inner pipe approx 2.5 inches diam. Outer pipe approx 4.5 inches diam. What are these seals called?

[John Rumm]

You want the whole concentric flue joint, or just the seals from one?

Either way:

[ss]

Its just the seals I require.