I had the exact same problem. I fixed it by going to an industrial supply store and bought some threaded rod with the correct threads (1/4-28, I think.) If you go with the hardware store stuff, you will have to use different lock nuts because the threads are different.
The industrial supply place had 3 grades of material. If I remember correctly, they were Grade 2, Grade 8, and stainless. I bought the Grade 8 stuff because it seemed to match the piece Van's included in the kit.
I bought a 3 foot piece for $5.00. It was the shortest piece they had.
Hope this helps.
Mark