October 29th, 2012, 9:51 pm
If he gave you dupe keys, vehicle owner has to be online so the vehicle spawns.
If car is owned by you, you don't know the location /myvehicles - /car find [vehicle ID]
If it says its inside garage or it can't be found for some random reasons, contact any admin in game with command /irc or /ask
To unlock and lock player owned vehicle use /car lock (locks and unlocks)
I believe this gave you answer to all of your questions.