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 Mutagenic Paste.
Doing this mission rewards players with Grade 6 Biochemical Samples, which include Mutagenic Pastes and Neurochemical Extracts. Since this is an "Abundant Yield" mission the amount of materials you get (without critting, of course) are anywhere from 2 pastes/extracts to 8 of each. If you need either of these items run these missions instead of the mission that rewards you with Compounds. Also since Abundant Yield missions are pretty much the lowest yield missions, if you have a Rich or Bountiful run them first. However you'll want to run Abundant before Moderate Yields.
In addition to acquiring the Mutagenic Paste 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
Mutagenic Paste Farming