Yes, you can buy past tutorials. I just did a few days ago. I bought my ss15 decks from a different vendor, but wanted to buy the upcoming tutorial on the flicker shot. I contacted support, and they opened a paypal invoice so I could buy it. I ended up also buying the sscc tutorial package of 2014 (perfect faro+cascade, 7-second pirouette, rubix opener, strobe, squeeze).
You could also buy the flicker shot tutorial when buying ss15 Virtuoso decks.
Send an email to: email@example.com
and tell them what you want to buy.
Note that waterwheel has not been released yet as a tutorial. At Cardistry-Con 2015, The Virts said they will release it when they know how to teach it properly. But the guys overloaded at the moment, so I would not expect that anytime soon.