That website I linked above has the OE parts for your engine & drive.
Sierra & GLM also make many parts for Cobras some of which are not available from BRP any longer.
To check the flappers you need to remove the exhaust riser. Drain any water out of the manifold first; also pick up a set of mani to riser gaskets. You will have to use some silicone spray and small screw drivers to pry loos the exhaust hoses ; they tend to get baked on. It will be a bit of a struggle. I use a hair dryer to heatvem up a bit.
The flappers are easy to install but it can be tricky to get the old ones out. I had to pull the drive to get them out.
https://www.dropbox.com/s/u3w9g3qvuxycb ... 1.jpg?dl=0In this pic, you can see the upper end of the Y pipe next to the big silver work light. This is from when I changed the manifolds last in 2011. On my boat I have the OMC one piece V6 manifolds so to get them off, I have to lube up the upper end of the Y pipe with silicone, loosen the lower exhaust hoses and slide them down so the upper ones will come off of the manifold/riser units.