I've completed my first research task , and came across this helpful resource to access past editions of web-pages:
Simply key in the name of the website you're looking for, and then select a date (down to the very day/month/year).
This brings you to a 'live' archive of the webpage and (sometimes) allows you to click on individual links within the webpage and access those links as you would have seen them at that time.
[If it doesn't work, different archived versions should be able to]
I've been able to successfully add them as sources - hope this helps!