Depends what mods you run.
If you have Nexerelin, 1000 + credit shortages for heavy armaments are very common due to invasions, and raids that take out space ports.
You can also create shortages by taking out convoys and smugglers, which do the same thing except you essentially get goods for free (except for the supplies cost in recovery and some fuel).
A real gamer move is to commission with a faction, and disable your factions enemy space ports, then invade and take over the market. Then you can shuttle goods there as the space port is disabled, making you mad cash as they will constantly want goods till the space port is re-enabled.