The correct website for Discount Dance Supply is discountdance.com. I highly recommend it. I have ordered from them and they are very good when it comes to returns.
Dancewear Solutions is the public version of Weissman's Designs for Dance which sells costumes to dance schools. To order from their main website (ordering costumes - not regular dancewear), you have to be a dance school owner. Their dancewear division accessible by owners and the general public. The only difference is the price of some items, usually about $5 difference. They are also very good and I would highly recommend them for general dancewear and shoes.
Another to try is dancedistributors.com.