I have some gimbled C3 lasers on my vulture which is going to the scrapheap soon, however these lasers are damn hard to find and I was wondering if I sold them would they appear in the station purchase list so one of my friends could buy them?
Short answer - no.
If you go back into Outfitting yourself, they will appear there for a short while for you to rebuy them in case you change your mind, though. A friend and myself tried to transfer equipment this way and it cannot be done, even though we were in a Wing together.
Interesting side point - the items you sell appear in the list at the same price you bought and sold them for. Whilst they are in the list, the same item will not appear for sale further down in the list even if the station sells it.
This might not seem like a problem however I have also found that when switching to new ships you get more money to play with if you sell off all your old modules first. If you paid full price for them and then want to fit out the new ship with the same (but cheaper) modules you have to fly away from the station into Supercruise, then go back and dock again to make the game forget the modules you just sold so you can buy cheaper ones from the station.