Not to take away any sources or ideas given above.. but the is another lower cost option....
There is an Amish outfitter that has fly front broad-fall trousers in up to 56 and will make larger on order... in Corduroy, canvas , or wool
colors are on the drab side ( blues, greys , and I think dark Burg. , canvas is in black, grey and natural which you could dye)
If that appeals to you I'll look for the address...