You should be able to take the bearings and seal to a good auto parts store, or a local bearing supply house to get them matched up. If you need a new hub, you might have to look for a trailer sales place or something local, unless you want to order the parts.
Most trailers are similar in the bearing setup. Usually, you snug up the retaining nut to 0 play in the bearing, then back off to the first place you can put the cotter pin, or lock, depending on the style.
I just replaced one hub, and the other bearings and seals on the other 3 wheels. Fortunately, for me, there is a trailer parts place about 20 minutes away. A $100 bill covered everything.