mid 2012 mac book and cs6

Hello,
I recently updated my mid 2012 macbook to High Seirra. Since doing this illustrator asks for registration and wont open. I no longer have a serial number i bought it so long ago, i've no idea where it is.
I have paid for a cc subscription and want to download and run CS6 through this. I've unistalled illustrator cs6 so i now want to reinstall cs6 and run though my monthly subscription.

Where is the cs6 download on the abode website, it's so hard to find! can i run cs6 through my monthly subscription without a serial number?