Gio,
Welcome back to the hobby, and glad to have you here. All you need to do is call the Tamiya office in California and ask them for a decal set. If you tell them it's for a really old kit, they may even send it to you for free. It's worth a try. They have sent me free parts and decals in the past. Try this number: 800-826-4922. Best wishes and happy modeling.
Barrett