What kind of clothes? Like a Hat, or Jersey, or regular shirt or something
Main stores: You can try (Modells or Foot-Locker)
Malls: You can try :::Kings Plaza "Brooklyn":::, ///// ::::Jamaica Avenue "Queens" <-- Not a Mall but a long strip with a variety of different little stores that might have what you want.
I don't know what area of New York your going to be in to give you exact spots, but Modells or Footlocker might have stuff your interested in.
I don't shop for Knicks items to be honest lol im sure someone else can give you other better choices if these don't help.
If all else Fails, Grab a Iphone and ask Siri