The catch is that the wood needs to be straight grained. If blanks are split from the billet, you will know if they are straight grained. If sawn, inspect carefully. You don't want cross grain. Lee Valley sells 36" dowels in birch, cherry, maple, poplar, walnut and red oak. I just made a rod starting with one of the red oak dowels, and it should be good.
Also, look for unwanted hockey sticks and garden implement handles. Sometimes rod blanks can be split from these.