Made to hold IV bags or water bottles, these things are freaking perfect for six 18 round extended clips. Comes with a shoulder strap attached and snaps on the back. (no MOLLE straps) The securing straps for each pocket doesn’t quite reach over the top of the clips – they're an inch or two short -- but for those inclined this can be remedied with some additional webbing or swapping in some shock cord. If you cut them off and reattach them they actually fit.
You can hang it over your shoulder - it even works over the top of a chest rig; for example you have 6x18 in your chest rig, and have this hanging on the side for an additional 6x18. I added a "waist strap" to mine and it keeps it secure against my body and doesn't move around.
The pockets are big enough that you can actually just squeeze three clips in each pouch for 9x18, but it's a bit snug.
They seem to average between 10 and 12 bucks with shipping on Ebay: search for "MOLLE II IV Bandoleer" or "IV bandoleer"