On my girls' first trip, I let them loose in Castle Couture (in MK- right across from the back of the castle) and let them pick out all of their princess gear since they'd be doing BBB the next day. I think Snow White was the only princess not sold in that store (at that time, her stuff was being sold over by the old Snow White ride)...but I think they may have all of the main princesses in there now. We got everything from dresses, purses, shoes, tiaras, gloves, wands, etc.
As magical and fun as it was to have them pick out all of these things in MK...World of Disney in DTD has more princess stuff than you can imagine! More variety of costumes, more accessories...you name it! So, if you can make it work...which I know you said you probably can't...it would be the very best option.