Where are you located?

There's a company called ProCast in Marlow, OK that does great stuff. I assume they could get it to wherever it needed to go.

Most of the column manufacturers all have a cast line now. I'd look at Chadsworth Columns and Melton Classics. Both are excellent in terms of customer service, lead time preditions and quality. They can give you small columns all the way up to 36" diameter columns. If you want to get into some really large columns, there is another outfit in La, but they usually only do 24" and larger concrete columns.

Susan,
Here in Florida there are many cast stone manufacturers. I've installed quite a bit of it from various companies. I would advise you to purchase from a source as close to you as you can (breakage, design). Make sure you have profile drawings showing exact dimensions that you want if you aren't using in stock pieces. Talk to your installer, most of us can look at a piece and tell if the molds have seen their better days, etc. Area masons sometimes know more than the architects, designers. After all we can usually tell whose shop it came from by looking at it.
Hope this helps, Brix