I worked at Camp Woodward PA last summer and will be working at Woodward Tahoe this summer. I have ridden and tested the roller skis. They kick ass. But I'm just going to answer some questions.
1) Can you grind on roller skis?
Yes, but it would have to be nose/ tail slide because 2 of the 6 wheels are directly under your feet.
2) How do you stop/ slow down?
Well, you don't really. In most cases though you are dropping into the foam pit or skiing a line through the skate park and once you get to a low enough speed you can just jump and 90 to completely stop.
3)Where can I buy them?
You can't. They're not for sale and are being produced specifically for woodward. So stop making threads asking and just go to Woodward Tahoe and try them!