The Wireman ( www.thewireman.com) a well known supplier of antenna making products for the amateur carries some 450 ohm ladder line which is much better than the standard stiff solid conductor line you see on eBay and else where. It has two 16ga 19 strand conductors and is very flexible compared to others. It is their product number 552. Full legal power and very flexible.
Most of the 450 ohm line out there these days has two 18ga solid conductors.
I highly recommend this line, you will not be disappointed !