Single wall to double wall collar...

Hey guys, quick question. I'm replacing an old Avalon Ranier with a newly purchased Jotul F100. I am installing a new section of 6" single wall pipe to go from the stove to the 6" double wall horizontal chimney section. I am having trouble finding a trim collar to do this.

The old trim collar (20yrs old) had a small flange that fit over and was screwed to the single wall as well as flaring out enough to slip over the end of the outer wall of the double wall pipe which it was screwed to as well to provide a secure connection. The collar serves both as a mechanical connection and for cosmetics and sees no flue gases.

What are you guys using and why can I not find this part anywhere ? I will use the old one if I have to, but I wanted to go with a brand new one.

Thanks!