Just wondering, can these be found in an existing save (from before installing LN), or does one have to start a new game in Bridgeport?

I've been wondering the same thing too. Basically, it depends on whether the existing spawner lists were modified ("Metals -- Medium" and so on).

I've been playing in Buccaneer Bay for the last few days, and last night my sim went on a collecting streak... and didn't find any of the new items. But it's hardly conclusive.

If it turns out that the existing spawners WON'T spawn the new items, though, all you have to do is drop a few of the new spawners in your hood.