RE: when it will be avaliable!
First of all, Welcome to Roadfood. Glad to see you post here. As far as the seasonal flavors of ice cream I think it depends on where you are and what companies produce seasonal flavors in your area. I can buy Breyer's Peach Flavor all year long...but the real Fresh Peach won't be in some of the speciality stores here until early July. (thats in the Louisville area).
I hope someone will respond about the seasonal nature of Black Walnut...I've only seen it in the "Factory-Flavors".