You can get them at the Japanese pavilion restaurants and perhaps at Nine Dragons. I'd check the allearsnet.com menus before you leave just to make sure.
First off, I adore both types of ice cream. Red bean ice cream tastes like... Well, for the exact taste you'll have to try it, but I can give you a "direction." Think of a pumpkin ice cream without the typical pumpkin pie spices added. It's creamy and sweet without being fruity. Green tea ice cream tastes like Japanese green tea with cream and sugar. It's
not like Chinese restaurant tea or American bottled green tea. But if you've had the green tea they serve in a Japanese restaurant you'll get the idea. If you want to start your taste test at home, Bigelow Green Tea (plain -- not flavored!) steeped for 2 minutes is a very good approximation.

Now I've gone and made myself crave red bean paste cakes and green tea. Where's my Japanese cookbook....