You want a 5mm hex that attaches via a 1/4" quick-change, correct? I did a quick google search and found that Ingersol Rand makes a number of 1/4" quick change bits, including the metric allen/hex that you're looking for. A good supply house should be able to get 'em. I have a metric set w/ 1/4" drive from Sears, but its not quickchange.
See their ad, page 3.
Linky Linky 2 Part # HXALK-9M