I was lucky enough that my La Peppina came with this gasket. I took some approximate measurements with my micrometer tonight in case this is any help. The outside edge of the gasket is tapered to match the shape of the kettle at the top. I'll try a little ASCII diagram to illustrate:
========(gasket)
\\ ______________________(lid)
\\
======(gasket)
The gasket at it's widest measured 103 mm and it went down to 101 mm at the narrower end of the taper (bottom). The inside diameter of the part of the gasket that overlaps the top and bottom of the lid is about 87 mm and the thickness of the gasket is about 6 mm.
I didn't take the gasket off to make any measurements. I'm going to wait until I have some Dow 111 lube before I remove the gasket again.
Looking at this some more, it looks like you should be able to get away with just placing a 4" flat round gasket between the top of the kettle and the vaporizer lid and then you could just tighten the vaporizer sandwiching the gasket between the kettle and the lid. I found a site (
http://www.brewerygaskets.com) that seems to carry these for brewing tanks (pretty close application) as well as some manway gaskets for tank doors that if you could get made a custom size (or cut down and superglue) would fit around the lid like the original gasket. Check out their 4" clamp gaskets and their manway gaskets. There's probably other places to pick up a 4" round gasket that you could use to sandwich between the vaporizer and the kettle.
Right now I'm trying to dial in the single basket for dose and grind with Ritual's Snowcone. My last shot was 7.5 g, almost to the top of the basket and it seemed to pull pretty well. I was surprised that I could fit that much in the basket as I was sticking to 12 g doses for the double basket.