Thanks. Well, I actually just went to HD (before reading this post). In another post I read you should not look for bulkheads in the plumbing section but in the electricity area. And indeed, I found them!! (Of course the ones that I really needed were sold out...). Well, at least I know where to find them. Oh yeah, they are also not called bulkheads but something like carfix.... (truly a name that didn't make sense to me.... on the other hand, I'm just a humble Dutch guy...)
I am familiar with Fish World. Also a neat store.