Is there a place I can get an executable Wireshark for Debian?

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All the packages are available, e.g in the Debian Packages Repository, but you'll have to manually fetch all the the required dependencies, unless you use something like Keryx to manage the offline repository (on another Debian machine that is connected to the internet).

You could also make a DVD or USB copy of the appropriate Debian repo and use that as the repo source on your target machine.

Note that it may be easier to get tcpdump installed on the target machine (less dependencies) and then copy the capture files to another machine for analysis using Wireshark.