There are lots of tutorials how to make two part mold on YouTube, so this short overview shows that these tutorials can also be used for fursuit making.

The first step (1) is to glue the jaw onto a flat surface with some hot glue. We seal all gaps around it with plasticine (yes, the stuff you played with as a child).

Then we build a box around it (2). You can use cardboard or acrylic glass like me. I just glued it together using hot glue, so that all gaps are sealed. Then you just pour A-Silicone (for example Rebound from SmoothOn) into the box so that the jaw is well submerged.

Once its cured you can remove the box and the plasticine. Now we have to cut so called "keys" into the silicone (3). This will ensure that the top and bottom part won't move when you cast a jaw. I just use a scalpel to just them into the silicone.

Now we have to reassemble the box around the mold (4) and seal it again with hot glue. I use a wax to cover the surface of the mold. This prevents the silicone I'm pouring on top of the mold from sticking to the bottom part. There are also special demolding spays for that or you just use Vaseline.

Now we just wait till the second layer of silicone is cured and remove the box (5). It might be necessary to use a scalpel to separate the two parts, though if you covered the lower part well enough the two parts will easily come apart.

Now we got a nice two part mold (6). I like to use different colors on the mold, it looking much nicer.

By the way, I'm not selling any jaw sets.