There is apparently some kind of Campy band that works, see here:
Doug Van Cleve Chandler, AZ USA
On 10/29/07, P.C. Kohler <firstname.lastname@example.org> wrote:
> It really is true: Edvard Munch's inspiration for "The Scream" were the
> words "French" and "Threading" in the same sentence.
> Seems Simplex's retrofriction shifters have a different threaded or
> sized mounting screw that doesn't work with their other band-on mounts
> like for the Criteriums.
> Does any have a band-on mounting for retrofriction shifters OR a
> complete lever/band assemby (either solid or open tear drop levers) they
> would like to sell?
> Please contact me off list before I run out of my vocabulary of French
> Peter Kohler
> Washington DC USA