From what I read here on the forum, the headlight switch must be pretty reliable, since I don't hear too many complaints about it.
That said, your best bet for a replacement (if it is needed) is probably a "roadworthy-challenged" W123.
Also I am impressed with the parts prices at Potomac German Auto. www.pgauto.com
I have not dealt with them but would consider it. Did not specifically see the headlight control switch in their searchable inventory but you know they have them - I guess its not a hot item - hopefully all the better for pricing.