Revert back to older version of Membership

Because of the serious bug and issues found in membership 3.5.2.9 I need to revert back to the previous version.
My latest ftp backup shows the changelog with this
== 3.5.1.8 ==

* Fixed: Critical issue preventing stacked 'finite' levels in PayPal Express gateway.
I need this zip file to revert back-- I cannot afford on a live site to be without the protected content-- also I cannot afford the time to "try and fix" something on a live site.

I am unable to locate in all my backups 162222_membership-3.5.1.8.zip
thanks
mike