I was not actively seeking out Sonic Drive In‘s Operating system in fact, this was just a pure random thing where I was watching one video about how to create your own in-house TV channel lineup and YouTube had recommended a video about Sonic Drive In OS, and of course, I had to check out the video. If you choose to download the operating system and install it, I assume no responsibility and you did this at your own risk.
Sonic Drive In OS dump: https://archive.org/details/SonicSSDImages