I used to prepare acute brain slice of locus coeruleus. The nucleus from newborn rat is very small (400um x600um approximately) but the cells are clearly visible under a microscope (20X). I would suggest to prepare horizontal slice of 400 microns thick (using the vibratome) then with a very small scalper try to isolate as much as possible the nucleus under the microscope (5X objective). It will be very small portion of tissue in order to have the desired cell confluency. Then try to digest the tissue and see how the cultures look like.
I did it twice and it looked like there were some big LC neurons but then I changed the project without trying further. But you might also try TH imuno-staining to see the percentage of LC neurons in your culture.
It depend how many cultures do you need you'll have to use more or less animals for it because LC is a very small nucleus.
Let us know how did it go and good luck!
Here is also an article, a little old but they did LC dissociated neuronal cultures.
Article Noradrenergic Neurons from the Locus Ceruleus in Dissociated...