I went through an exhaustive search while working on my own suit last year. I thought, perhaps, it was a stretch grosgrain ribbon, pieced together and (as near as I can figure from the high res images) topstitched. I never found anything that changed this opinion.
In the end, I was afraid that the stretch grosgrain wouldn't have enough give for the spandex I was using; I didn't want to shred suits the way SJ was rumored to have during filming. While poking around the local fabric shop, I found some herringbone-textured fold over elastic that I thought would work really well, providing a similar texture and the "channeled" look of the original:
It was a little wide, but I was reaching "must sew" mass, so I went for it. During construction of the suit, I stitched it three times -- a zigzag on either side, and a straight stitch up the middle. I'm sure I popped a few of them in the course of the con, but everything stayed in place and still looked pretty good:
I haven't seen the stuff in any local stores again, here or back in the US, but I have the catalog information, if you're interested.
Your previous version looked pretty awesome, so I'm curious to see the "improved" suit! =)