FYI, JetPack is a collection of packages to make life easier for someone with an Ubuntu host. The individual packages are still available. At this time, the most recent L4T for TK1 is R21.4, downloads here:
[url]https://developer.nvidia.com/linux-tegra-r214[/url]
Feel free to ask about which packages you need for which purpose, but the most common need is to flash the Jetson with R21.4. This requires the “Driver Package”/“Jetson TK1”, plus the “Sample File System”.