It's important to put some care into the eyes on your maquette because that's what people look at and that's what makes them look real. Where do you get the eyes for maquettes?
There's a range of available options, depending on the quality you want:
1. Making eyes out of Sculpey or Fimo (oven hardening modeling material). The simplest solution is to model spheres of Sculpey and fire them in advance. That way they're hard, and they won't get distorted when you work them into the sculpt. Sculpey is available on Amazon.. Tip: you can also model and fire the teeth first, so they don't get all soft and distorted when you're building the mouth.
2. Plastic stuffed animal eyes (back row, left). These are available at craft stores, and they come in a range of sizes. I haven't had a problem yet with the plastic melting, though it's a risk, as the curing temperature of the Sculpey at 275 degrees Fahrenheit begins to approach the melting point of the plastic. Animal Eyes 30mm on Amazon
2. Doll eyes. (back row, center) For humans, the plastic doll eyes are flat-backed, and come in brown and blue and are very inexpensive at craft stores. It's a good idea to test these in the oven at curing temperatures to make sure they would survive. There are sources for higher quality glass doll eyes available from the online doll supply market. Good sources include: CR Crafts
3. Solid black plastic eyes. (back row, right) These are solid black, but surprising realistic for a lot of creatures. 12mm solid eyes on Amazon
4. Glass taxidermy eyes. (all the ones in the foreground). Glass eyes used by taxidermists are extremely realistic. You can get the ones intended for birds, reptiles, rodents, or large mammals, so you can imagine the range of sizes and colors. A good source is Van Dycke Taxidermy Supply.
Please let me know what sources you've discovered.
There are lots of other practical behind-the-scenes insights about maquettes in my new instructional art documentary (watch the trailer on YouTube) about the making of the Australian dinosaur stamps.