Don't have one, but I believe Optech makes one that works on the SQ-Series. One of my SQ-A bodies came in a box with the original strap, still in its plastic bag. In all honesty, it looks pretty narrow to sling a four pound camera around one's neck for any length of time, so maybe you don't want an authenticke one anyway!
I didn't bother getting a new strap for my sq-ai when i purchased it. I instead went to the hardware store and found two metal rings (think keyring) that fit through the hole in the post. After that i used an optech strap and it works like a charm. I think the whole thing cost me $.50.