I think VDO did make speedos for both, right? There probably should have been some speedos in the recent 70's thread, as they were a very popular accessory. I had one of those IKU superlight speedos with the little red plastic wheel for a while. That was probably the pinnacle of mechanical bicycle speedos. They disappeared instantly when the Avocet cyclometer came out.

RE the OP: I think you'll just have to keep looking on ebay and asking around, and hope you get lucky.