there are four borders in san francisco: union square, stonestown, SF center, and the one by the ball park. having just purchased my reader at the one in SF Center, i know they have a few. The union square one is planning on getting more any day now, and the guy i talked to on the phone when i was looking for mine said stonestown had a whole mess of em. they'll hold stuff for 3 days in advance, so if i were you i'd just use
www.bordersstores.com to find the one nearest to where you'll be staying, then call ahead and have them save it for ya.
they generally also stock the cradle and the covers, so you can grab those there as well.