You can get flex hose in the 2.5" from your local auto store, autozone, napa, etc.
It comes in aluminum or a PVC, I prefer the aluminum.
Look for flex hose used on old truck intakes, sometime napa has it. Or you might be able to use dryer flex hose for the 6x4, might have to check that one.
Use a couple zip ties or band clamps to hold in place.
It's cheap and easy to find.
Check morris4x4 if you looking for the official stuff.