How to attach a flanged intermediate pipe to a flangeless catalytic converter?

I'm having to replace my exhaust on a used car. I found that the catalytic
converter had been welded originally. The previous owner cut it to put a
"new" intermediate pipe/muffler/tailpipe on (even though it was rusted to
hell).

Since the catalytic converter was welded, there's no flange. The new
exhaust system has a flanged intermediate pipe. How can I attach this
without welding? I am unable to find a flanged "sleeve" to clamp onto the
catalytic converter outlet pipe, but maybe I am using the wrong
terminology? I can't use those flange repair kits since the outlet pipe doesn't
have a flared end.