If I'm reading this correctly, you're talking about stealing various items from special ships.
This can be done with përs resources; an individual ship you might come across occasionally. But, looking at your posts you talk about stopping a convoy and stealing from them. That could also be done.
You could have a mission controlled by a crön, not something you could accept or reject, but something that randomly goes off on it's own. It would give you a limited window of opportunity to hit the convoy, which opens up a few other possibilities which I'll get back to later.
The mission could be programmed to have one special ship, and a goal of disabling and boarding; giving the player (You - not u) a mission cargo. The mission could be scripted to succeed once the player lands after boarding the ship. Other ships in the convoy could be handled with Aux Ships.
On success, the mission could, as you said, grant a voucher (using the command (Gxxv)). Then you would have some "Prototype Weapons", whose outfits would only appear on (Oxxv), and on purchase would execute (Dxxv). This means you only get one of these special items for each time you hit a convoy.
Getting back to using cröns instead of a normal mission:
Remember all those rumors that you get from hailing traders? When you hit "Greetings", they send back some message or other; usually "I hear prices for Luxury Goods are low on New Ireland." You could change some of the standard responses to rumor mongering: "You know, sometimes there's a bunch of Federation ships going through the Nesre Secundus System; like they're in a hurry to get somewhere." or "On the fourth and fifth of each month, there's some tech convoy that stops in at Rauther. It makes you wonder what they're carrying."
You could also have a përs ship drop these little bits of info for you, in it's Comm-quotes or Hail-quotes.
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