I have a mission to supply fine meals.
At first i looked for argnu steak. No trader had it.

When i found a trader with argnu stakes i bought his whole supply.
Every trader since then had argnu stakes.
Then i found, after some searching, a trader with rare spices. And every trader after that had rare spices.

So youre system is buggy as hell. Yes because i have stuff, traders "suddenly" all have supplies.

This whole deliver stuff mission type kinda sucks. It breaks any immersion you have. Basically its it terrible.
Because it is buggy as hell.

Now no trader has "mixed fruit" but i bet when i find one, every trader after will have mixed fruit for sale.

Sounds like a bug.

As far as I know, noone from the developer, Egosoft, ever comes here to this subforum. They love to hear about bugs and problems so please report on their forum, or if you refuse to use that, send them an email. Remember to be informative and polite.

I think there may be other ways too, maybe Reddit.

Sorry, but you need to collect those things as you go along, from the beginning of the game. I always grab the Angu steaks, rare spices (funny, they are the least rare of the three things needed) and mixed fruit that I see, as well as the pilot seminars from any station I'm on. Trying to gather them up after accepting a mission is the hard way. The fine meals are one of the keys to getting 3 star plus pilots.