Fancy sneaker company Concepts, which has locations in Cambridge and on Hudson Street in New York City, hosted a party at the W on Saturday night to unveil its latest special kicks, a collaboration with New Balance that celebrates a long-running baseball rivalry. The “City Rivalry’’ series has a New York model in teal and a Boston version in red and gray suede. Both models come in a Cracker Jack-like box. Last we checked, the NYC model was sold out, but Boston’s shoe, which sells for $219.95, is available starting Monday, which is also Opening Day at Fenway. You can find the shoes at the Concepts pop-up store at 19 Yawkey Way at 9 a.m, and at the Harvard Square store at 10 a.m.