Missions are not an efficient (or cost effective) way to acquire gathering resources for grinding the appropriate crafting skill. The only missions you should be doing for gathering skills are the ones that net you the required additional generic components for crafting that you can't gather in the field (and only otherwise obtain from the crew skills vendor).
Green Goo is a level 1 material and should be available from every level 1 node. It's the equivalent of Desh for Scavenging - the most abundant material. As I said, you just need to return to your capital world and do some harvesting. Aside from Slicing, all gathering nodes are on about a 4 minute respawn timer, so if you do a circular sweep of an area (much easier in Coruscant, given the cityscape layout), then by the time you get back to the starting point all the nodes should have respawned. Especially bio nodes, as that isn't a popular skill from what I have seen.