I have never had this problem with other crew skills, but I cannot get Mutagenic Paste in any kind of quantity.
I don't think I'm the only one, either, given what it goes for on the GTN and the fact that the other grade 6 biochemical samples can't even be given away.
As other's have stated, there are some items that simply do not pop enough for their required use. Farming is the best sollution. An hour of farming will solve the problem for you by providing you with a multitude of said item.
Check out the comments over in Torhead for information as to the best farming zones. Just put "mutigenic paste" in your search list and you will see Torhead come up in the list. Trusted site, player comments will show you the way.