Go to Google maps and search for a nearby: supermarket, pharmacy and drug store, art and craft store, costume store OR community theater (run two searches).
Write down the phone numbers and addresses for the nearest three stores in each category.
Call the supermarkets. Ask if they carry Knox gelatin. If they don’t, ask if they carry sugar-free Jell-O. Circle the address of the nearest one that carries Knox, and if not Knox, then sugar-free Jell-O.
Call the pharmacies. Ask if the carry liquid glycerin. Do NOT accept talking to the register worker; they will often have no idea so ask to speak with the pharmacist if you can.
Then ask the pharmacist if they carry medical adhesive. Double check that the adhesive is for attaching pads and tubes; NOT “wound glue,” as you are not trying to superglue a paper cut. This is less common at pharmacies but worth asking for.
Ask if they carry sorbitol syrup for diabetics (this is a long shot and unlikely but OK not to find).
Circle the address of the nearest pharmacy that has both glycerin and medical adhesive. If none carry medical adhesive, then just go for the glycerin. (You probably won’t find the sorbitol.)
Call the arts and crafts stores. Ask them if they have moist “stone” pottery clay, and plaster of Paris. If you couldn’t find glycerin, ask if they have glycerin for soap making, or could refer you to a soap making supply store.
If you couldn’t find medical adhesive, ask if they have costume kits with “spirit gum” in them. If the employee has no idea what that is, say “the little devil horn kits with tiny bottles in them” and see if that rings a bell.
Call costume stores. Sometimes these are seasonal so you will have to find out if a seasonal store is near you through spirithalloween.com or a similar chain website.
Ask if they have spirit gum, medical adhesive, or pre-done gelatin blocks (could replace the sorbitol, gelatin, and glycerin and skip you right to the mold making).
As a last-ditch effort, call a community theatre and see if they'll lend you some spirit gum or medical adhesive. You could also use liquid latex to stick gelatin to your face. It applies just as in the video. Call back the costume store about liquid latex alone or in a kit.
Now, buy the materials. Give yourself about 2 hours to roam around town if you live in an urban area and have a car.
Sculpt. Don't dwell so much on being artistic that you don't give yourself enough time to get this done!
Cast with plaster. This has a 2-hour set time if made with hot water. Cast a small amount in a paper cup to test. If it's not set in two hours there's been a problem, such as poor mixing or too much water.
Mix, heat, and pour gelatin into the plaster mold and let it cool.