I'm cheap so these are the low-cost ideas, although when I have seen columns at the flea market they were more than what I wanted to pay.
architectural salvage yard
flea market
utility company? maybe they have some old poles you can scrounge. trim out and paint.

Hi there~

I'm new on this forum, but I frequent the Garden Junk site. I would say that you could find the posts at Lowe's or Home Depot type stores. They aren't cheap though. You may be able to find some where they are tearing down a building, etc. Good luck in your search!

You could also make your own. There are cylinder shaped tubes at Lowes or Home Depot. You could fill them with a hypertufa mixture in the place you'd want them, and you just tear off the tube (it's cardboard) when they've set. I've got a garden book around here somewhere where the garden owner did that and painted them different colors. If the columns were left alone, you could encourage moss to grow on them.

Holly

Thank you everyone! I think I'll try my hand at painting/aging my own. I'll be sure to post pictures of the final project!! :)