Well you aren’t going to find pants with the grey spots, that’s for sure.
I would go with either scrub pants or loose sweat pants for a base. Scrubs can be found at uniform stores, medical clothes stores, or places like Goodwill or Salvation Army. You could find sweatpants at Walmart, Target, or maybe Goodwill but they may be in bad shape.
Once you find good pants with no decoration and that fit you right, either take fabric paint and paint on the grey circles yourself, or cut out pieces of grey fabric and sew them onto the pants. Both look good when done carefully and cleanly!