The manufacturer of Line-Lok Tent Cleats is
You would want the CL266 I think. They work well as long as the string is thick enough. 1 mm is OK, but 0.5 mm spectra won't grip. Funny about that.
As far as I know, everyone else is reselling from that company.
(Disclosure: I have corresponded with the owner of the company, but that's all.)