Early on I used a few online suppliers, but lately I’ve been buying locally at “Sculpture Supply Canada” who also have a website at https://www.sculpturesupply.com/ and do mailorder. I don’t remember where you are located but there’s a very good chance that you can find a local supplier. Sometimes even arts and craft places stock this stuff and if not, could certainly order it for you.

I will add that almost all of the plastics and silicones that I have used are products of https://www.smooth-on.com/ who I think will also do mailorder direct if you don’t find any other options.

For starters I’ve been really happy with the putty silicones, which is fast and easy to use and pretty “idiot proof” (so it was great before I understood the processes). Now I mostly use Dragon Skin silicone, but that works best in a vacuum chamber, which is going to cost you $500 – $1000 new. You can do it without a chamber but you’ll make more mistakes and won’t get as good detail most of the time.

BTW, the “basic craft kits” might actually be an economical way to get your feet wet and try the different materials in low quantities.

As to sculpting the masters, I’ve done just about everything but most of the time I work in epoxy clay (ie. products like “Fixit” and “Apoxie Clay”) which is a two part clay that cures chemically rather than via heat. Sculpy and Fimo (which is heat cure, in a home oven) also works fine but I was never really able to get good results from it personally. With the epoxy clays I found that you could both get good results from sculpting itself, and from subsequent carving after the fact with both hand tools (even a knife) and my Dremel. And you can also bulk it up with multiple layers, which doesn’t seem to work as well with sculpy/fimp (it falls apart in my experience, and doesn’t handle multiple cure cycles that well). If you like working with a Dremel, invest in a flex shaft (about $50)… It’s worth every cent.

If you like carving another option is wax. Some people swear by it. Another option is “3d collage”. That is, taking found objects and modifying them. If you remember some of the rings that I made out of toys, that’s how I did those. You can also take a cast of an object and then modify it. That’s how I did some of my “zombified” versions of Nefarious’s Littlest Pet Shop characters — I made a copy in hard plastic resin, which I then carved and modified with clay, and then took a second mold from my modified version.

All in all there are tons of different methods to create your master and all of them have pros and cons… ultimately it all comes down to what you find most comfortable personally.

Finally, I’ll add that with those silicone molds you can also use them for casting soap (incredibly easy to do) and wax candles, as well as food (candies, jelly, cakes, whatever) to say nothing of lower temperature metals like pewter (although for pewter and perhaps other metals you have to use “platinum cure silicone” because the “tin cure silicone” off-gasses when you pour metal into it and you end up with bubbles in the surface).

Whew, that was a lot of typing. All in all a lot of these questions will just answer themselves once you start playing with it. If you can afford to spend a couple hundred dollars to get some different clays, some plastic resins, and some silicone for the molds, you will have a lot of fun and learn a lot.