Polymer Clay is available at most craft stores and there are several brands to choose from. I've tried most of them, but my favorite is Living Doll and Super Sculpey. Both products are made by the Polyform Company that makes Sculpey, Premo and Souflee products. It doesn't really matter, which polymer you like to use, they all have more or less the same properties.
I'm particularly fond of Living Doll and use it primarily in portrait commissions and gallery sculptures. I like the finished texture, color and strength of the clay. The Sculpey Brand commissioned me to create two pieces to use on the packaging of two skin tones of Living Doll clay and I'm very proud that these images sit on the shelves of craft and art store around the world.
Most polymer clay companies have local and national distributors of their products. In Canada I use The Polymer Clay Shop at https://www.thepolymerclayshop.com/, in the USA you can order directly from Sculpey at www.sculpey.com and internationally you can find a distributor in your country at https://www.sculpey.com/1-international-distributors
For tools and accessories like eyes, armatures, beads etc. I recommend www.morezmore.com Here's a little bonus for you, use coupon code FishWithFaces at check out and you'll get an additional 10% off your order.