If you're looking for yet another place to get your new $35 Chromecast, give your local Best Buy a ring. At least one lucky fellow was able to successfully buy the device from a Best Buy in South Carolina. Calls placed to several stores would indicate that's not the only one. However, most stores are expecting stock to arrive in the next day or two.
Full-size Best Buy stores are getting 20-30 Chromecasts in the first batch – high-traffic stores may get an extra allotment. If there are no stores nearby with stock, the Best Buy website also lists the Chromecast now. Whatever route you take, the device is $35 just like it is from Google Play.
The Chromecast has free shipping from Best Buy, but you'll still have to pay tax. Maybe this will tide you over until the Nexus 7 ships.