If you run out, Chris, I think I have more than 20 meters of real good quality dial cord which even looks just like the original 
If anybody needs it, I'm willing to send out some at cost + postage (it isn't that expensive per meter, but really hard to find nowadays and I can only get it in full spools - therefore I won't start a charity operation even though I'd like to).
In a pinch, the classic "Bear Brand" black string by J. & P. Coats (probably available at a cloth/fabric/sewing shop near you) will work. It stretches quite a bit more than real dial cord, but usually works quite well if you prestretch it before tying the final loop. Some people use fishing line, but I've always found it too slippery for B&O which usually has a very small diameter pulley at the tuning knob.
And boy, would I like to see some videos from the 60s/70s on how the these cords were strung at the factory! I'm sure they didn't spend half an hour or more per unit to get it right, like I do 
