Why don't you try the Vermont Wildflower Farm?????

I believe these people might be able to help.

I don't know which species to suggest, since you have posted to a site used mostly by americans and my experience is in the US. However, once you have determined which wildflowers are suitable for your site, I would recommend that you consider putting plants in the field instead of sowing seeds. Sowing seeds in a field with established grasses and other plants probably will not work well. I would select a few types of wildflower that are suited for the climate and location, which are perennial, and which will spread by themselves once established. I would obtain plants from a source in France, and put the plants in the field in a location that is suitable, and position them so they look like they have grown there naturally. Winter and spring are good times to do this. Hopefully, the plants will thrive and spread. AS you become more experienced, you can plant a wider variety of species until your fields have the number and variety of wildflowers you would like.