Sleepycat was acquired by Oracle in 2006. The product is still available under the original open source license and continues to expand. You can find the source code on the Oracle website here in .zip and .tar formats. The distribution includes the complete source code.
Just FYI: Oracle has a lot of open source products. Source code is available to everyone.
Disclaimer: I am a product manager for Berkeley DB and have been working with the product for more than 7 years, so I'm a little biased .:-)