I’m looking for a mod (or default replacements or magic ) that would make it possible to sell the plant you can grow in the plantation station career reward (no idea for its proper English name, but sims can use it to produce this plant, and the station is visible on the right), and the cowplant in an owned business.

You'd like to be able to sell that pwetty plant that grows flowers on your shelves? (Hydroponic station?)
I turned a few things into buyable long, long time ago...I might be able to look into that particular one(s) since if I recall, the flowers it produces comes in many colors. But I just got back into TS2, and just yesterday as i was all done with 6 new recolors for my pajamas mesh, I realize I do not remember how to recolor my own stuff. lol
Yes, you can laugh at me, I'm OK with it.
I got it though...after a few coffees. So I might be able to help as long as my knowledge agrees to cooperate and come back to me.

I do have an extracted version of that plant as a stand alone object. I can try and find out where it came from if you like. You don't grow it though.

It’d be great to have the actually grown plants possible to be sold, but if it isn’t possible, I could get the stand-alone one and pretend it was grown (i.e. after restocking I’d remove one of the grown ones from my sims inventory with testingcheats, so I wouldn’t get additional money).
As for colours, as I can recall it’s always been pink for me.

buyable Hydroponic Plant Pot by HugeLunatic