"Cartoon Feud," the Teen Titans Go! and Scooby-Doo crossover which aired in October, is now available for purchase on DVD as on March 3 (must have missed the memo on that one, sorry!) The episode can be purchased on the Teen Titans Go! Season 5, Part 2: Smells Like Magic DVD. Unfortunately, you will get 25 other Teen Titans Go! episodes along with it, so if you don't like the series I would recommend skipping this release. So far, none of the other crossovers like this have been released on DVD, so if you're a huge purist, it may be worth it for you.
Here's a link to this DVD on Amazon.