JC,
I don't know how available it is, but Rome Cable shows
"ROME COPPER WEATHERPROOF LINE WIRE POLYETHYLENE OR XLP COVERED
APPLICATION:For use on insulators for overhead circuits."
It goes as small as 10ga. From the specs
http://www.romecable.com/Catalog.htm (See spec 1215)it appears to not need a messenger.
To answer your other question, Rome also has this coated MC:
"ROME INTERLOCKED ARMOR POWER CABLE,600 VOLTS
3 Conductor,Rome-XLPE Insulated,Aluminum or Steel Armor Type MC
APPLICATION:
As 600 volt Type MC cable rated 90C in wet or dry locations;for installation aerially or in metal rack,tray,trough,cable trays,or direct buried" (See spec 7455)
