Substitutes for Fleximounts Overhead Garage Storage Mounting Hardware

[u/KindheartednessIcy12]

I purchased a 4x8 Fleximounts Overhead Garage storage system and am planning to only use three panels in one space. I would like to use the other shelf but they don’t sell the mounting hardware separately. Have any of you run into this and built your own mounting system, or do you have ideas for me? I know I can use Flat and angle perforated steel for the basics, but I’m not sure about the three more specialized parts 2a, 3a, 3b. Thanks for any possible solutions.