Here are two good places to start.
www.easternmarine.com and
www.championtrailers.com. I ended up with the Kodiak S-CAD disc brakes. I got most of my hard brake lines and fittings from other places as the "kits" as offered are designed around one size fits all vs a custom fit. I will have some pictures and more install details in a few weeks. I got all my parts except three short hard brake lines and the fittings at these two dealers.
The more I got involved, the more I wasn't impressed with the factory rigging. Except for the main brake line from the MC, I am replacing the entire system. I also decided it was good time to just replace my Dico/Titan 10 master cylinder vs. rebuilding. You will also need a blocking or bleeding solonoid and a flex line at each caliper with the conversion to disc brakes.
I am also going to use the Buddy Bearing axle seal kits as I already have the SPINDLE - LUBE® spindles. These seal kits gives you a new "speedi-seal" type cover and a flat surface axle seal. We have had good success these seals.
If you are launching in salt water, the whole Buddy Bearing type system might be worth the investment. The Spindle-Lube or Buddy Bearing system also allows you to not have to hand pack the bearings. Just install dry and pump in the new grease.