Hi Christopher,
By default you only have access to older versions that your licenses would have entitled you to. So, if you had a license for a year, but failed to renew, there would be a gap in the available downloads covering that period.
The last release we have that is marked compatible with WordPress 3.6 was the 3.5 release: you can grab old versions of The Events Calendar itself from this page and I’ll happily provide you with a link to the matching Events Calendar PRO release in a follow up post.
Please understand though that we cannot provide technical support for such old releases, nor can we guarantee you won’t be introducing problems that were subsequently fixed.