I use a standard football needle for my Mag family forks, BUT.... I modify them first.
In my experience, the diameter isn't the problem. It's that most ball needles feature a cut window near the tip, in the side of the needle. This, and the relatively flat point on the needle wears at the air valves.
I cut off the tip of the needle above the side window, and chuck the needle in a power drill. I turn the tip with the drill between 2 blocks of steel, pressed together in a "V", or in a right angle corner formed by 2 pieces of metal. This way, you can slowly form the tip into a blunt hemisphere with the hole in the centre. THis seems kinder to the valve.
If you do bugger the needle valve in the fork, you can make your own replacements by moulding 8mm diameter cylinders from RTV sealant. I use a wooden block 16mm thick, drilled with 6 or so 8mm dia. holes, and greased inside the holes. I cast the RTV sealant into the blocks, allow them to set for a few days, then press out the cylinders (vice) and trim their ends. The best ones are then run thru lengthwise with a sharpened spoke (forming the "valve"), and then they seem to perform as well as the now unobtanium old valves.
Good luck!
J
