You can get them at both. For the one at Veilstone City, you go to the house above the pokemon center (I don't know which one) and have an empty space in your party. The person will give you a Porygon.
I have five Porygons, one from Veilstone and the other 4 from the Trophy Garden. You have to talk to the rich owner of the house and he will say a pokemon's name. If it is not Porygon, you have to wait for the next day. Then, the butler will tell the Rich Person that pokemon is not in his garden. The Guy (Is it Mr. Backlot?) will tell the butler to put them in. It takes a while to find them, though.
« Last edited by ShadowVulpix2 on Jan 26th 2010 »