Hi Irina, Thanks for joining the effort to expand low FP eating! You have some good ideas. I think your assumption about honydew having a similar FP as cantaloupe is a good one.
I first go to the USDA National Nutrient Database site first to investigate nutritional facts. For products, I also try to get an actual food label or image of one on line. Nutritionaldata.self.com is my third and perhaps less reliable source.