Happijac has their own website that you can buy the brackets and some replacement parts. Most everything else will have to be ordered through a dealer as LCI will not sell directly. It's rather interesting that you just started this thread because I am in the same position as you - well similar anyways.
My toy hauler has the happijac system installed and it came with a drop down bed and a "U-convert dinette." Problem I am having now is that my new "toy" (Polaris RZR) is too darn tall to keep both the drop down bed and drop down dinette installed. I am going to have to remove the dinette lift.
I was hoping I might be able to replace the dinette with fold up seats on both sides. I'm figuring that I am going to be losing the space because of height but I should still have quite a bit of room on the sides. I would like to utilize the happijac lift instead of mounting fold up couches on both sides. Any one know where to find this type of furniture? If not then I might be doing some construction work in the near future!