I been wondering myself about the carbon fiber rods so I did some looking.
Tower used to carry one size but it's discontinued.
Then I found this.
http://www.kitebuilder.com/inventory/grahpitetube.htm
They have several sizes. 4.6 mm (.179 inch) OD fits inside the 4mm corro plast ribs nice and snug.
If that doesn't work, email me private and I'll re you with the link.
Or just go to kitebuilder.com and look for their products and price list.