As in my title really, Where do you get gaskets for mongoose ex or other 3inch jobbies?

I have a mongoose in my garage which i have cut out flexi and have a new one i am going to weld in, dont have any gaskets tho and when i went to motor factors, he just pulled his face and said

"what the bloody hells that off? we've nowt that big!"

Also seeing as we are on exhaust type business, I can get my hands on

a downpipe with flexi type from a lad local to me for 40 quid, whats the consensus on whether i should get it off him for said amount, and take off my one piece Probably ebay downpipe previous owner fitted?

Only thing putting me off is its a bit of a bu88er of a job access wise.
