Check out mojosgear.com (no relation), they look to have a pretty decent assortment of dyneema cordage. 0.8mm, 1mm, and 1.25mm unsheathed dyneema line are all available. 1.5mm is the smallest listed size they have available sheathed, although I suspect the 60-80kg rated stuff w/ dyneema core is probably between 1-1.25mm:
Note the minimum order requirement of 100 meters (and it's not mix and match, either).
Disclaimer: I have no idea if these guys are legit or not. Can't find them on reseller ratings or BBB...