STYLETHREAD -- LET'S TALK SHOP!

I can't tell you where to find one, but I can assure you they exist. I bought one a few years ago at a huge electronics store in Paris while I was traveling for business. Actually I still have it, though I hardly use it anymore.
Did you check ebags?
You might also want to consider those rolling laptop bags. We all have laptops where I work and I see some people with those. One girl who used to work here had one for that same reason (back problems). HTH!