You shouldn`t need an activator for leafmould. Unlike compost containing fresh green leaves (which decompose through bacterial action) autumn leaves are broken down by fungal activity, and the main necessities for this are (a) to get (and keep) them wet, and (b) to keep them in close contact with each other.
If you have a relatively small quantity then you can achieve both by cramming the leaves into plastic bags, filling the bags with water, tying them, and then, after a few days, making a few cuts in the bags to let out the surplus water.
If you have a lot then you would be better to make an enclosure of posts and chicken wire - preferrably about 4 ft deep. Pile the leaves into it, soaking them after each 12inch layer, and repeatedly pressing them down, then stick some sort of cover (wood, old carpet etc.) with a few bricks on top to weight it down.
The bag method will probably produce leafmould in 12 months or so, while the enclosure method will take a couple of years, but in neither case will an activator make much (if any) difference.
