Yes, CS6 extended licence is still sold. You probably have to call Adobe customer service to get the answer how much extra it will cost.
Thanks for your reply! That's good news, as I was sure I'd be told I'd have to move to a subscription service (since that's what Adobe is pushing towards). I wonder why there's no option online to upgrade CS6 to CS6 Extended. Ah well, crossed finders the upgrade isn't too much.
I hope you can get just what you want.
But if you can't, ask yourself: How many months of $9.95 subscription could you buy (what does an Extended upgrade cost? $300?)?
Could you buy the subscription a year at a time, and invest a few hundred dollars in Adobe stock and pay for the subscription for an even longer-term?
And you'll get better 3D support in Photoshop CC.
Just food for thought.