I'm looking for a gown or evening dress for my mother?

She's going to be a primary sponsor in a wedding, so I'm pretty much her stylist for every occasion but I can't find the right dress for her! I shopped at Carson Pierre Scott, Macy's, Nordstrom, Lord & Taylor, JC PENNY, Marshalls, a bunch of department stores, wedding stores, little retail stores at the mall. I can't find anything! She's around 60 years old and I'm looking for a dress thats a little conservative but also very flattering. Anyway does anyone know any good websites or stores I could check out? We're also on a budget so anything less than $200 !! hehe THanks guys :)