does anyone know how to get a cranidos?

The Skull Fossil necessary to revive a Cranidos is available only on Diamond and Platinum, so you'll have to trade for one. The easiest way to do that would be to use the GTS and offer a Shieldon for a Cranidos.

There are two ways to get a Cranidos, by getting the fossil from a friend or by trading in the GTS. Be on a lookout--in the GTS some of the Pokemon offered are holding the skull fossil, in which can be turned in to the fossil guy in Orebguegh City.

CH Out

If you have a action replay there is a code that will allow you to catch enemies Pokemon so you could catch it of the first gym leader but you are proberly past that bit

First, you must have at least 1 badge. Then,you go to enterna city and go to the house beside the pokemon center. There talk to underground man, you will receive an explorer kit. Go to your bag and press a button on the explorer kit. You'll go to underground. There, you will meet roark the first gym leader. After that you go back and talk to the underground man. Go and completed taska from the underground man and soon you can use hammer and pickax to search the wall at underground. Soon enough, you will find a fossil. There is one fossil called the skull fossil. Once you had it go to the orebugh museum and talk to the man on the receptionist desk, choose the skull fossil. You go out from the museum and go in there again. Talk to the same man and you'll receive a cranidos lv.1 and when you trained it up to Lv.30, it'll become a ramprodos. Good Luck!