You can use a different plug as long as it's rated for the amperage of the breaker. Remember that breakers must be rated for 25% greater than the draw of your kiln. So your 30 amp kiln should be on a 40 amp breaker, which is why it's using a 50 amp cord. 40 amp plugs are not very common. You should get the 50 amp Orton setup, even though it's a little oversized. That way if you ever upgrade to a larger kiln, you can still use that controller.