Subaruparts.com
part number 8 on diagram-Exhaust gasket (2) 15.90 each part #44022PA021
part number 15 on diagram Bolt (4) 2.98 each part #44059AA010
part number 16 on diagram Springs (4) 6.90 each part #44028PA000
part number 17 on diagram Nut (4) 0.53 each part #902350004
This is for the spring bolt setup for the front of the 2-1 cat. If there's anything else you need, subaruparts.com has excellent diagrams to see parts. Just create an account with your email and password and don't worry, they do not spam.
For the rear of the 2-1 cat
part number 10 on diagram Exhaust Gasket (1) 16.84 part #44022PA031 and you will need 2 each of the spring/bolt/nut from above