95% of my Intarsias are made using 3/4" stock. I do have some 1-1/2" on hand, but seldom have need for it and if I need thinner than 3/4" I'll rip or sand down the 3/4" stock to the thickness required.
Each time I go to a big box store or lumber yard I'll spend a few minutes looking for boards, especially Poplar and Cedar, that are unique in color or have grain patterns I think I might need and pick them up while available.