Exhaust Silencer Tdci

The middle section silencer on my defender is nearing the end of its life and will need changing sometime this year. I have got a new silencer on the way so it will be on the shelf ready. The pipes on the silencer connect to the front exhaust section and rear section using thick flanges and bolts (three bolts at one end and two at the other end). This has the same type of connection as the TD5. I cannot find specific gaskets which fit between these flanges anywhere (but can find generic types). Are gaskets normally fitted at these flanges or are they just assembled with a slather of joint paste? I want to have the parts on the shelf ready and not have to go shopping after I pull the old silencer off and find they have them.