Getting materials for raising your professions is easier than you could have ever imagined in Swtor. With the Crew Skills feature they have in the game you can gather materials for any profession while doing anything. All you need in order to make this work is a few credits, some spare time, a companion and to follow these simple instructions. I recommend that you read this guide if you're not familiar with how missions for Crew Skills work.
Now the best way to gather materials for any profession is by running missions. There are 5 or 6 missions available to you through each Gathering Crew Skill and for most Mission Crew Skills. You will always want to run the higher Yield Missions first when it comes to gathering materials this way. Below is a look at one of the missions that will reward you with Immunity Cell Cultures.
Doing this mission rewards players with Grade 6 Biochemical Compounds which are Immunity Cell Cultures. The amount of Immunity Cell Cultures that you get from running this mission without a crit ranges anywhere from 2 to 13, which was the most I ever received from running a mission like this. Depending on what missions you have available to you though you may want to check their yield rank, if you have a yield higher than abundant such as Bountiful or Rich run those missions before you run an Abundant one. However you'll want to run an Abundant Yield mission before a Moderate.
In addition to acquiring the Immunity Cell Cultures through running missions you can also gather them the old fashion way, by actually going to a planet that has nodes of those items. For Grade 6 materials there are only three planets players can go to, Ilum, Belsavis or Corellia. Ilum offers the most nodes out of all three planets although it has a tendency to get over crowded as everyone knows it is the best planet for farming these materials.
Below are some of the best farming locations I have found for Grade 5 and 6 Bioanalysis materials
Immunity Cell Culture Farming
Farming Grade 5 & 6 Bioanalysis Materials on Belsavis (Republic)