This artictle has good instructions for getting Google Alerts RSS feeds:
To use the feature, log in to your Google Alerts account and make sure you have at least one entry. If you don’t, create one by picking a search query for Google to track for you.
Next, click on Manage Alerts and hit the Edit button on an alert you want to get an RSS feed for. Under the “Deliver to” option, change the option from your email address to “Feed.” Hit the blue Save button.
The Feed option will change to an RSS link, which you can then copy and paste into your favorite RSS reader. For example, Google generates this one for the query “The Next Web.”