Okay, if the collective generation isn't a primary goal, then playing cards would be my suggestion as well. To spell it out in a little more detail than @
ad_hoc: build a deck of 18 cards and deal them out into six piles of three. Sum each pile to get your six ability scores. You can tune the deck to get the power level you want. [Three 1s, three 2s, three 3s, three 4s, three 5s, and three 6s] will produce results equivalent to an average 3d6-in-order roll. For arrays that look more like the 4d6-drop-lowest method, there's no perfect deck, but I recommend something like [one 0, one 1, two 2s, two 3s, three 4s, four 5s, and five 6s].
Or if you think using cards instead of dice is just plain wrong for D&D, you can also normalize dice-generated ability score arrays pretty easily. First, pick a target total or point-buy value or whatever other measure of power level you like. Second, create an array using any normal dice method. Third, roll 1d6 to randomly select a score in that array and add 1 (if the array is below the target) or subtract 1 (if it's above). Repeat step 3 until you've reached the target level.
