Dale937 and oldbluetruck did what I did on my '36 Chevy pickup. They made their own.
All it takes is some kiln dried wood of your choice and a table saw. A lot of guys like oak and even Home Depot has that in all kinds of widths and lengths. Other, more exotic woods are readily available too in urban areas. I used vertical grained fir and it still looks very presentable 45 years after it was installed.
Why pay somebody to do the simple task of running some wood planks across a table saw to rip the width and grooves and cut the length? Another benefit of doing it yourself is you get to hand select every piece of wood instead of being stuck with what somebody sends you.
