look for a dimension cross disc or kona p2 disc fork. make sure you get the one for a road bike not mtb. they are relatively inexpensive at ~$70.
Look for a used front wheel(set) on craigslist first. Sram Courier cranks are outboard bearing so you won't have as much hassle with maintenance
Avid BB5 or BB7 road disc brakes will work with road levers, and the regular BB5 or BB7 work with mtb levers
I did the same thing you're planning on doing with my Crosscheck
