Hi Sally,
Great question!
Many calendar applications — Google Calendar and The Events Calendar are both great examples of this — provide an iCal (or “.ics”) feed.
This format is pretty much the industry standard for letting other applications subscribe to calendars and is one of the methods that Event Aggregator supports.
On looking at the first URL you shared (for a calendar generated by Evanced) I don’t see any clear links to such a feed, so the best I can recommend is that you approach either the support team for Evanced or the owners of the sites you wish to import from and seek their advice: if such a feed is available they should be able to provide the correct URL.
That said, based on the information provided in the other topic you linked to, it does seem like it might be possible to “craft” the URL you are looking for, much as the other user did, but unfortunately I seem unable to determine what that should look like.
With that in mind, reaching out to the owner of those other sites/calendars may be your best shot here 🙂