I was going to suggest what Jenava and Marianna said - I've done both before and it worked well.
What I've noticed more often is that the Nordstrom inventory program says that they have a certain item in stock in a store in my size, but they only have *one* - but sometimes when there is just one left, it's hard to track down on the sales floor.
That being said, I've certainly had sales assistants at Nordstrom who were willing to go to great lengths to actually track down the item in question, so I have no complaints on that front!