Yes there are.
Use Pokemon transfer.
The other games have porygon to.
Pearl and Diamond: Trophy garden. (After you beat the game)
HG and SS: Celadon City (After you beat the game)
It is in White Forest in the first also
Trade it through GTS or GTS Negogations.
Pokecheck or AR <The least recremended.
Well yes. The only ways to get porygon in gen v are to catch in white forest in white, catch it on dream radar, trade for it, or use poke transfer. So, try to find it on dream radar.