Goat Hill Photo is great for slit film; I haven't tried their splitters. You can use 16mm movie film. Also microfilm; here's an approach I got from a Subclub user some time ago. It's for Agfa Copex microfilm at ISO 50, but best to avoid high contrast situations:
Mix a Sodium Sulfite solution of 2 oz Sodium Sulfite to 1 liter of water. Mix 2.5mm of HC-110 (concentrate, not stock solution) to 200ml of Sodium Sulfite solution. Develop for 6 min at 68 degrees F with agitation every 30 seconds.