any suggestions of what might fit? advice ...
thanks in advance
Have you found a solution yet? If not, here is an idea. Don't know about the availabilities of the oem CS/CSi horn contact rings, but they do require less modifications. Buy a contact ring unit from a steering wheel from the 1980's (E24 here) and with minor modifications, should make a perfect fit. They are the same diameter as the Petri rings and still available at less than $10 each from BMW.
Start by slicing off the cone part of unit by a hacksaw or a Dremel tool with a cutoff wheel, then file flat. Next, find a thin and rigid plastic and cut to the same diameter as contact ring. Drill out center to accommodate steering wheel mounting spindle, grind down flush a plastic pin that sticks out on base of ring unit and finally make a small cutout on new base to fit electrical contact tab. Position ring unit on top of new plastic base and epoxy together, drill 2 holes to plastic to mount the new modified unit to the Petri alloy hub. Done and for less than $10!
The ring mount holes are on the inside of the narrow Petri hub, hence the relocation of the E24 hub outer mounting ears.