The 1978-P Lincoln Cent is very common as the Mint struck over 5 billion examples. Finding one in circulation should be very easy. Even finding examples up to about MS64 condition should be fairly easy. Examples in MS65 are also abundant in Uncirculated rolls at a small premium over 1 cent. In MS66 condition they become a little more challenging to find but are still easily available. In MS67 condition they are very hard to find and command a substantial premium. Most MS67 rolls have probably been found in the past few decades in original rolls, mint sets or bags.