i am currently on an earlier mission for the fighters guild where i must find ecoplasm or whatever can anyone tell me the best place to find it

You need 10 pieces right. The way i did this is go to one of the ships in the dock at Bravil (The Ships called the Serpents Wake) where you can accept a quest to get a Ladys crystal ball, (She will be on the ship and when you talk to her you can recieve the quest called The Ghost Ship of Anvil), and you can battle ghosts there and loot them for Ectoplasm.
There is also a Fighters Guild mission at the same rank you're on i think, or a previous one, where you go into a cave and its filled with ghosts that all carry ectoplasm. Just accept all Fighters Guild Contracts that you can at your level until you get that one or track back to the cave if you've already done that contract (The contracts called Unfinished Business and the cave is called Fallen Rock cave). These 2 quests should both net you 10 ectoplasm.

You can also buy them from alchemy shops in just about every town, there is about 1 or 2 at each at a cost of about 32 gold i think, so you'd probably have to do some travelling if you did it this way.
Or like Lyn said you could do some adventuring into ruins etc, but this will be time-consuming and not every ruin will have a ghost in it. (Ayelid Ruins would be your best bet if you were to do it this way)...

Hope this helps. I was lucky as when i did this Fighters guild quest i already had those 2 locations set in my mind as the places to get the ectoplasm so it wasnt too much hassle...

If you are still looking for ectoplasma, go to the church in Bruma and get into the basement. You will have to pick the lock in order to do so but there are plenty of ghost down there guarding the place. Fight them one on one if you can to make it easier and try to do this before you get to level 20 cause you will have to deal with wraiths instead of ghost.

If the church in Bruma is not the right one then go them all. Hope this was helpful