I'm a bit confused as to why you specified a vintage strop. It's already been pointed out that you take a big chance on buying any old strop - and I don't see that vintage necessarily means better quality.
I do have quite a few older paddle strops that are travel size - these can be picked up pretty cheaply and are good for kamisori sized blades. I've bought these on the basis that if the existing leather is shot I still have the paddle itself that can be re-covered - and as Thaeris pointed out, you can get some old ones with ivory handles.