Does anyone know what they are called and who sells them? They are grooved pieces of plastic or something that fit in the ribs of bed liners to hold stuff from sliding around.
I tried searching on-line, but I'm coming up empty.

 

Normally bedliners are fitted for 2x's. 2x4, 2x6" or whatever your application happens to need. Another option would be the cargo bars, either ratchet or shower curtain style. The last option I've seen is Loading zone's cargo gates, they are expensive, but very nice products.

Now if you barrow a rail system or use trac-rac's system there are a few other options available.

 

To the OP, I think you're talking about these, Bed Bugs Bed Liner Cargo Stoppers . I have a set, and they're alright. Not great, but ok. I think you'd really need 4 of them (one on each corner of what you're hauling).

I'm not entirely happy with them, I think I have to find another way to secure cargo back there.

 

Yes those are what I was talking about. I was thinking of useing them to keep my compressor from rolling back and forth. I Have it tied in with a rope from the front tie hook to the back tie hook, but it doesn't stop it from rolling. I also have a small tool box to keep in place. So i think i need maybe 6 of them.