If you have read it carefully it clearly says that it will be released later this year. So you will find no repository yet
Open Source Later this year Swift will be released as open source.
Swift’s unique combination of elegance, power, and safety has the
opportunity to move the entire software industry forward. It is
exciting to imagine what we will build together
Late year update:
www.swift.org
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solved Where is the Open Source repository for Swift 2.0? [closed]