I found a Rolleiflex strap on eBay from China. I think it's the real deal although it could be a high-quality knock-off. The scissor-clips seem solid and authentic, and the leather they attach to says "Rollei" on it. The strap itself is webbing, about 1"-1.25" wide, and has a decent rubber back-of-the-neck pad. It was about $40 including shipping from China, which took a reasonable 7-8 days IIRC.
I have seen good remarks on the forum regarding these traditional replacement straps with the alligator clips. Good luck...