On Fjodur you can find it in North-Eastern Balheimr. Just destroy the rocks, but keep in mind that not all of those rocks do give you Condensed Gas. Only the ones that look a bit unusual and are placed in the weird green water like substance. Best to bring something that protects you from heat, because it's very hot there.
Genesis, Lunar biome. Take an anky, any normal looking rock you smack will have a small amount. Anky can also get ele sharts and Ambergris from the green glowing lunar rocks. Spawn Lunar East, in one of the craters there's a small cave with loads of rocks, that leads into a chamber with water, fish, seekers, featherlights and occasionally a Karkinos, you can get loads of gas in there without the sun radiation or meteor strikes.