Check, bazaar, transmute yourself, or find one of the many circuit paths of scrap iron spawn points and realm switch. There are plenty of fansite-i.e. Wizard101Central-guides that give specific locations and routes.
Chelsea court, after you get of the airship take the first right you come too. Go all way to end there is a area there where you can go back and forth, change realms. Also west clockwork tower some players swear by going in and out of the first room you will get a lot too.
The best way to get scrap iron is to go to Marleybone's MUSEUM, to the Counterweight East dungeon - you go in and you fight what's there on the first room - there is a scrap iron spawn there - keep going out and back in - fastest way to get it that i know of.