Have searched extensively for free versions of archived software. Some links resulted in software downloads from not so trusted sites.
You can download most of it from
http://www.oracle.com/technetwork/database/enterprise-edition/downloads/index.html
You need an account to download, but the accounts are free to create. (Not 100% sure on what level of access that gets you though).
Older versions are there, but can be hard to find - you just need to hunt...