Head over to an awning manufacturer or a boat cover manufacturer, and give them the dimensions. Allow an extra inch or two to make it easier to get over the top of the columns, and have them install a very long brass zipper the entire length of the tube that they will fabricate. I suggest Sunbrella material, and having the top of the column cover reinforced on the underside. Shouldn't be that expensive to have made up, and the Sunbrella comes in many colors.
I have both the Maxjax (thanks Gabe) and a Bendpak 4 post lift. You can't beat the quality of either, and they have made my life a lot easier, as I have gotten older.

Junkman