Years ago, I got some at the airport, from a company that catered to one of the airlines. You could consider importing it, say from Puerto Rico. Also, a dry ice plant is no big investment, considering the scale of course.
You need to ask if you can buy CO2. Then you can make the machine to turn it into dry ice yourself. Many years ago I worked with a load of boffins at a science company and they would turn it out for me when I needed it for stage stuff. I seem to recall they would turn the cylinder upside down and let the gas jet out as liquid into an insulated box. It was that easy (I think) - or did I spend too long sniffing laughing gas?- I really can't remember for sure. - Anyhow DIY is the answer.