The whole issue is from the place that Nvidia gets thier gpu manufactuered TSMC and they have fallen behind with production so Nvidia is left waiting for their gpu shipments to come in so they can put it on their cards and ship. They have also started looking for alternative places to get thier gpu's manufactured and I read an article that said they were trying to work out a deal with Samsung to produce some of their gpu's. TSMC has also said they are expanding production facilities to accomodate more product so all this may take a bit to do and sooner or later the stores will be supplied with enough cards to make everybody happy.
Nvidia just anounced the GTX 690 and I'm thinking that those can be scarce as well.