It is very common here in the frum neighborhoods and cities of Eretz Yisrael that tzedaka organizations will hold once in a while, large sales of goods at very cheap prices. Once it will be shoes, another time clothes, before the school year begins it might be school supplies and school books, etc. It is a very big chessed and helps a lot of people save a lot of money that they could use for other things instead..

Ladaat reports about a sale that is run annually by the tzedaka of the Vaad HaRabbonim that for whatever reason was delayed and did not happen in its usual time, and instead was delayed until now and they wish to have the sale now, during the "Three Weeks", rather than wait until later.

Not knowing what to do, they went to Rav Elyashiv and to Rav Chaim Kanievsky with the shailoh if it is ok to have the sale now.

Both rabbonim answered that it is allowed.

Ladaat does not go into detail explaining the reasoning behind the hetter given by Rav Elyashiv and Rav Kanievsky, but I suspect the reason is because during the Three Weeks (not during the 9 Days portion of it) one is allowed to buy things, just one is not allowed to make the bracha of she'he'chyanu. so normally we would say don't buy anything that requires a she'he'chyanu, though really the buying is allowed, and the buyer should delay wearing it and making the she'he'chyanu until after the Three Weeks is over. Perhaps we can add to the logic that there was a "tzorchei rabbim" in play here as well, as it is a specially cheap sale to the public (and not for profit).