That does not look like an MTD model number who now supplies the parts.
The blades are too short if it is leaving grass between blades. Unless, someone rigged that deck onto that mower. The deck might look perpendicular to the frame but the blades are supposed to be at a slight diagonal to the perpendicular.
You do not want to buy a new deck. Search Ebay or Craigslist for used deck. Ask in CL wanted section.
Another link you can try: