Microsoft Stores:
https://www.microsoft.com/en-us/store/locations/htcvive
GameStop:
http://www.gamestop.com/gs/pages/events/HTCVIVE-Demo
Micro Center:
http://www.microcenter.com/site/content/VRReady.aspx
HTC Vive has got their production working, and if you place an order your unit should ship within 72 hours. Whereas with Oculus Rift the expected shipping date is in August:
http://www.tweaktown.com/news/52441/htc-drops-bomb-oculus-vive-orders-now-ship-within-72-hours/index.html