Hi. The particle size is very large so dispersion is difficult for a long time. But you can try some surfactants like triton X-100 in water or siloxane-based surfactants in nonpolar organic solvent. Maybe it works.
I also think a viscous liquid is required. However, it is not just a question of viscosity. There should be a yield stress: large enough to suspend the particles, but small enough for the mixture to flow easily. This principle is often used in various cosmetic and household liquid products that contain solid particles. Specialty chemical companies offer various polymers for such formulations.
You can find some further information about the technique in: Colloids and Surfaces A: Physicochem. Eng. Aspects 288 (2006) 165–169.
As you mentioned, your system is probably difficult to formulate because the particles are quite large and have a high density.