Disclaimer: This page contains various affiliate links that provide a small kickback to me, at no additional cost to you.
For furring:
https://www.lowes.com/pd/Roseburg-1-4-CAT-PS1-09-Square-Structural-Plywood-Douglas-Fir-Application-as-4-x-8/1000015971
https://www.homedepot.com/p/SANDEPLY-5-2mm-Sandeply-Plywood-1-4-in-Category-Common-1-4-in-x-4-ft-x-8-ft-Actual-0-205-in-x-48-in-x-96-in-479023/203414042
Grainger in Seattle for 80/20 and Amazon for flat profiles
15-series
https://roostvans.com/wp-content/uploads/2020/11/EUAI-170LowerMount-Rev112220-Web.pdf