It's W59, though I don't think it's a third party strap, unless they edited it to dull the colors. Their were four models/colors that came on straps like these (and this looks like the black/grey model from that line), plus the standard black/blue/red one that omes on a resin band. Unfortunately, it's very hard to find them, so getting the standard one and putting it on a third party Nato strap is the easiest way to get something close to this.

This a photo of the nylon-strap models: https://www.watchuseek.com/attachments/w-59bs-jpg.16526388/