Your diagram can be found here
Checking Husqvarna, it appears they have discontinued Husqvarna 525568403
Shutoff Plate (Reference #2 on the diagram linked above). They show to have replaced it with: Husqvarna 525568303
Rate Cam & Chute Assembly $9.19 (Reference #4 on the diagram linked above).
Another alternative would be to order the entire hopper, as it states it includes Reference numbers 1A-4 on the diagram linked above (which includes the discontinued Shutoff Plate.
Please feel free to contact our Customer Service professionals at 1-877-798-7278 if you have any further questions!