Finding synonyms for uncommonly used words like "interstratify" can be challenging, but here are a few options to explore. "Intermix" is a commonly used word that shares a similar meaning, referring to the blending or mixture of substances or elements. "Interweave" also works, as it suggests the interlacing of layers or materials, much like the process of interstratifying. Another option might be "commingle," which refers to the act of combining or mingling things together. To really show off your vocabulary skills, consider using "intercalate," which also describes the process of alternating layers or inserting something between others.