If you look at fig 1.5 the rear roof panel ( 7 1/16" on both sides) and then fig 1.6 the rear panel 4' 6.5" add them together .
Comes to 5' 1 3/4" ( 61.675) add 3-6" as a safety margin.
Best figures I came up with by looking at the plans and the picture of the rear section. If not call coleman directly or a dealer, the Coleman Cobra was being sold 2 years ago at a ebay store.
Also I second the quest outfitters route when you need replacement or making your own poles.