The Spring IDE sources are available from this Git repository: http://git.springsource.org/spring-ide .
Alternatively, you can install the Developer Resources features from the STS update site: http://dist.springsource.com/release/TOOLS/update/e3.7 (uncheck "Group items by category").
Note that some features such as the form based configuration editor are part of the commercial SpringSource Tool Suite which is free but not available as open-source.
HTH,
Steffen
Steffen Pingel
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Committer, SpringSource Tool Suite
Senior Developer, Tasktop