If you can't find any
Sepp Holzer grain, try winter rye. The only difference I've heard of between the two is that the Holzer grain might be a bit taller on average. For my rye, it seems like the biggest factor in how tall it gets is how loose the soil is. Really hard packed stuff will get me mini 2 foot tall stalks. Loose soil can produce stalks over 7 feet.
My rye was originally collected from the stuff the ministry puts down on roadsides for erosion control, so it's nothing special.