Don't you have a gunsmith anywhere near by?

He should have tons of them laying around.

Or even a gun shop.

If you don't have a gunsmith around just call Remington and order them. 800-243-9700
They are $3 each.

Part numbers are
20601 for the front and 20606 for the rear (12 ga)
20602 fro the front and 20607 for the rear (20 ga)

At numrich they are $5 each and Numrich will charge you about $15 for shipping and handling. Jack First is a little better on price and shipping but Remington is your best bet if you don't have a shop that has them.