Lots of places have wildflower seeds— you can find lists from Wild Ones for instance or your local UMass Cooperative Extension.

These lists are only good if you understand your growing conditions (shade, sun, soil type), and how much work you want to do to establish and maintain them i.e. watering, weeding, thinning.

Here’s a good list of resources:

https://ag.umass.edu/resources/home-lawn-garden/fact-sheets/flowers

I’ve had great luck growing Purple Coneflower from seed (if you’re looking for something easy to both start and maintain). Sunflower is also super easy to grow and will flower in one growing season.

In general starting from seed can be tricky — it helps to have a weed-free bed and to start them in late fall so that they establish themselves early in the spring.

If you plan to direct sow them now, you should look for varieties that do not require cold stratification (periods of freezing and thawing). Also you shouldn’t expect flowering until next year (or late summer/early fall) if you plan on starting perennials. There aren’t a whole lot of plants that will do much in their first season, other than annuals.