I applaud your enthusiasm for seeding wildflowers. You will want to winter sow the seeds late in the season or even after the ground freezes and ideally before it's covered with snow. You will likely want to include some prairie grasses in the mix. The University does not maintain a list of seed supplier but any local nursery should have seeds, or online. It is very important to control weeds in particular in the first few years. Attached a link for much more detailed information: https://extension.umn.edu/planting-and-growing-guides/planting-and-maintaining-prairie-garden#care-after-planting--1644215

Good luck with your project the birds and bees will thank you!

Paul -Master Gardener volunteer