Check with NAPA, they sell combination shims that are 2" wide and varies degrees of angle. Check your local store for part # 704-1161, 1163, 1165, 1168 (2" wide, 1,2,3,5 degree) Joe
Search on "caster adjusting wedge". The online part numbers are different now, since the last site "upgrade".
No need to do Ebay or Speedway. Just walk into the local NAPA as 4woody said and tell them what you are after and take the numbers he provided along. You need to figure out how much angle change you need first though. As someone else said, they are standard fare at most 4X4 shops. Not to pick on FNG's but there are other places that sell parts for our cars besides Speedway motors.