I'm wondering if it doesn't have to do with State regulations...I had someone from another state, don't recall which, call me about where to find liquid Chlorine. They couldn't find it at any pool places, etc. There may be some law in MO regarding the public sale of liquid Chlorine.
Have you checked at any chemical supply houses?
The guys at the pool place should be able to help you with the mix ratio of the powder to get the strength you want.
If not, get the specs on the powder, and I'm sure we can help you here.