You get 2 type of key always (gold + windgate) that are sold. And you can get at least 4 of key in Garnodat dungeon if you picklock (heavy, prison, gear, skull - at least). So if you have iron or brass key left, you can do Garnodat dungeon for key.

You need 7 (gold + windgate) and 5 other types of key.

If you really do use keys all up, there is console "spawn" command as a last resort.

I have already completed the garnodat dungeon (and used most of the keys) so that's not really an option, I think I have given 5 keys + a lockpick, so may end up having to resort to the console command for the last one. but I really appreciate the responses, thanks!