There was probably a commercial solution but it was far more fun and less expensive to make my own adapter.
It consists of ring made from a piece of steel electrical conduit with a 4.25″ inside diameter, just about perfect for the Profoto mount with the rubber ring and clamp removed. I welded the ring to a piece of sheet metal cut to fit the mounting bosses on the Speedotron 102 head. Three screws through the ring retain it on the Profoto mount.
The heat from welding disturbed the surface of the metal so the adapter doesn’t look like much – a coat of paint would resolve that – but it works great.
More photos are at my Flickr site: