Speaking as a Brownie leader, I'm puzzled. Have you been asked to supply all this colour-coordinated kit? Most packs have stocks of camp uniform which they lend to the girls, and/or permit the girls to wear their own clothing at camp. The (ahem) joy of Brownie uniform is that it's distinctive and it's not easy to find the same colours in the shops.
They have uniform to lend out but it seems to be discouraged to use that unless you really (financially) NEED to borrow kit. Obviously, week to week, DD only needs one set of uniform, not 5xshirts, 3xtrousers, etc.
We were given a pack list and there definitely wasn't a tone of "We have everything you need here", but rather "We do have some uniform items we can lend out".... We can afford to buy, I just like to be frugal, am busy snapping up stuff on Ebay.