There's a limited supply of non-corn syrup Coca-Cola in the US. It's the "Kosher for Passover" formula, released every year starting mid-February to early March (it's long gone by now - sorry). They change the cap colors as an easy indicator...

There's usually an annual article in a major newspaper about the Coca-Cola "purist" who buys a pallet-load to last him the year...

If your local supermarket doesn't stock significant kosher for passover food products, try to find the name/phone number of the nearest Orthodox Jewish synagoge and asking them for suggestions about where to do passover food shopping!