Sak,
Century Wheel in Wilsonville has the parts you need. Switch to twin disc brakes, you will need a new coupler or master, new hubs, and new brakes...but, safety first, do not go cheap.
Here are some pics of my re-braking job from a Northriver Alluminum Trailer:
Old Brakes and hubs
Old Coupler
Axels removed and replaced (I had a bad spindle, so I replaced both axels...safety first)
New Axles
New calipers...Kodiak
Both done...including brake lines for the second brakes.
New Coupler, with new disc brake master cylinder...much nicer!
All in all it was a full days job for two untrained nimrods (my brother and I)...and that was including replacing the axles. The coupler was one of the more difficult jobs because the brake line had to be re-routed, and that was a huge pain in the keester!
It was also a little scarry working under the trailer, on all four jack stands...but it was amazingly stable...and yes, we had additional fall protection just in case (my skull).
Could not be happier with how she works...full salt water package also....a must.
Good Luck