The design “Robusto Brilliant” is still available via Ultratec if you Google ultratec robusto. But in that article, Jim does not suggest it for dark garnets. Another reference for a design for dark garnets mentioned his design, “Derek”, which is available online from Bob’s Rock Shop list of designs. A search of other internet sources quote him as saying the secret to dark garnet is to use a step cut pavilion.
Let us know what you find out!
Sue