dispersant isn't an issue in the US....
....there's loads of it readily available. The issue is whether the oil is amenable to dispersal. Once it has "weathered" (i.e. the volatiles have evaporated and it turns that horrible brick red color, or into tar balls, forget it. Dispersant won't touch it, and it is cripplingly expensive to apply from an ADDS (Airborne Dispersant Delivery System) pack.
Additionally, much of the oil is trapped in the subsurface current.. the dispersant is a surface technique..
Pinkman