The LS/3 woofer cabinet is just huge 9 foot internal volume box,(8.82 cubic feet) with two huge ports tuned to 30Hz. If one had the resources to build a pair of cabinets, it would seem rather easy other than the cost of material.
You're doing what I've been wanting to do for some time, clone a Fostex LS series monitor. Except I was going to start from the woofers and go from there. I have the L475s, but I don't have the resources or the room to park a pair 9 foot cabinets. So that idea is scratched...
If you find cabinets, you'll also know where a pair of L475s are at.
A guy can probably cobble up the proper crossover networks.