My mother is 5 feet tall and weighs about 95 pounds.  Shopping is frustrating because it's difficult to find petite sizes that are small enough to fit her.  She is willing to make minimal alterations, but would like to at least attempt to find something that might remotely be a good fit right off the rack.  
Any suggestions on where to look?  I have already looked online at Nordstrom and some other department stores... Slim pickings.  She is looking for a long gown.  She'd like to be able to try before she buys (so, no online-only retailers).
Thanks!