I have a list of Brighton based Sea Fencibles somewhere, so if I can find it, I will have a look at it for you.
Don't hold out too much hope though, for as I understand it, The Sea Fencibles were predominently fishermen formed into a sort of anti-Napolionic home guard on the shoreline. As Napoleon's forces never got here, the capture of any of them during those duties would have been unlikely.
Roy G