It would help if you told us which Panerai you are interested in.
Some GMT autos were, until recently, available with the same ETA movement that Panerai used... but the supply of these movements seems to have dried up. History.
Panerai used the ETA "Unitas" 6947 in many of their hand-wind watches... and that movement is easily obtainable, both as a gen Swiss item or an Asian copy. Of course Panerai reworked the Unitas a bit... mainly to make it prettier.
Panerai are rigid in their control - spares of any kind are close to unobtainable ... your chances of finding a genuine, Panerai-modified movement are so close to zero as makes no difference.
But if you insist on having a gen Swiss 6947 movement in your watch, you can buy one from Ofrei... last time I looked, they only cost $75. Put it in a closed-back Pam and nobody will know...
Having said that, I have loads of watches with 6947 movements, both genuine Swiss and Asian copies.
The only one to let me down was Swiss.