There won't be anything available at Walmart.You'd have to order a true milk paint or soy paint online for paint,and for a seal you can find natural DIY recipes with a quick Google(just be sure the ingredients are hamster safe of course).Not every paint is safe for hamsters,and even "non-toxic" products can still be harmful to hamsters
You could also do a berry based DIY dye and then use a natural DIY wood seal as mentioned above,which would make it entirely DIY so the ingredients could probably be purchased in store making it a lot easier!