Hallo,
Not an expert here, just some of my notes for you no specific manufacturers’ colors. The paint section of the store you mentioned should have chips for your use. Also, just for views of shades / tones go through your favorite spice aisle and check out the ‘natural’ color values you find there.
Less is more I discovered.
Colors: Trenches and Blasted Zones in General
Base Color
Muted Earth tones and shades—essentially, your choice of mud.
Middle Lights
Lighter values of mud, dust, mushroom, and sand, these would include various values of ocher, sienna, umber, and cinnabar.
Muted greens to dark green (even dusky blue-greens).
Heather / Dusty shades of rust, rose, and yellows (ocher, sienna, and umber especially).
Highlights
Woodash, cinders, achromatic-grays, some lighter shades of blue
I used various chalks, powdered paints, and varieties of ground-up sands and pumices to add textures and tonal variations to my trench board. These were available from garden centers and hobby stores and nature. Add hammer and you have a good supply of resources, perhaps even cheaply.
Best,
Sender