I would talk to your dist. about possibly buying the balls you think will sell and returning any that don't. You'd have to put up the money, but at least you could get credit if they don't sell.
We don't have a lot of sales through the youth. Most get hand me down balls, because their folks don't want to invest in an activity they may not stick with or may grow out of. But if as you say, this type of tournament generates sales, then I'd carry the Hammer Doom line; Anger, Toxic and Doom. Great balls at a good price point, in 14 and 15lbs. If you think its little kids then I'd stock a couple vibes at 12 and 14lbs. Skip 13lbs all together.
Stocking balls is difficult because they are very expensive, go "out of style" so fast and there's so many weights. Its just not possible, for us, to carry in stock every ball in every weight.
Erin