Not sure where you are in KS -- looks like Wichita -- but we do have them here in Roeland Park, at a Price Chopper that specializes in Latin American products. You might try asking at a grocery store in the correct neighborhood.
Now that I think about it, I've also seen them at Tienda Casa Paloma, a local restaurant that has a small grocery section.
You might have luck asking a farmer at your local farmer's market to pick a few blossoms from his/her squash plants and bring them to the market to sell to you.
I've never seen them in a grocery but I don't think you would as they are flower-like i.e. fairly delicate.