Since you are coming at he end of March pretty much everywhere be having sales. I don't know what kind of boards you like or dont like so I will just list every place I can think of.
Paragon Sport (867 Broadway btw 17th & 18th)
- largest variety and inventory snowboards and all related gear. Likely to have their 30-40% off sales going too
Burton Flagship Store (106 Spring St, New York, NY)
- Its the Big B. Likely to also be having storewide sales
Homage (64 Bergen St, Brooklyn, NY)
- never shopped there myself so don't know exactly what kind of stocking they have
Blades Downtown (659 Broadway btwn Bleecker & 3rd NY, NY)
- very limited selection but often have very good sales at the end of the season. Don't even waste your time going to Blades on 72nd st. They are almost exclusively a skate store.
Dicks Sporting Goods (240 New Jersey 17, Paramus, NJ)
- so so stocking. Really depends on the location. The one by me out in long island, NY has a decent sided inventory
Emilios Ski Shop (112-28 Queens Blvd, Forest Hills, NY)
- located in Queens. Has some decent inventory. Might not be fully worth the trip out though without calling them first.
Rei (303 Lafayette St, New York, NY)
- much like Dicks, it depends on the location. The one I just gave the address for is pretty good but I dont know how they are when it comes to sales.
There is one more new store out in the Union Square area thats like a few doors down from this comic book store called "Forbidden Underground" that has a small selection as well. I can't think of their names though.