Sourcing seeds and plants for large berms

I want to build a few very large berms to block the road, possibly as early as spring. There would be several hundred feet of 8+ foot berms. I would like some ideas on sourcing enough seeds and plants to immediately plant as soon as I am done. I will be saving the top soil to put on top, hoping for a bunch of regrowth and dormant seeds sprouting.

I was at a campground the other day and saw a bunch of dandelion seeds just outside the mowed area, so I filled a grocery bag. This got me thinking about my berm project. I plan to make collecting seeds this summer/fall a priority. I know of a 2 year old clear cut that will have huge amounts of mullein seeds this year. Any suggestions on seeds to collect? Preferably these would be easy to collect in large amounts.

What about sources for buying bulk seeds? I think various large bags of bird seed including sunflower would work well.

I may cut some hay to use as mulch when done hoping I get a bunch of seeds. After the berm is mulched I may try to transplant things such as wild strawberries and lilacs.

Thanks for any suggestions

Check any local feed or farm supply stores.  They usually have good prices for their 50 pound bags of seed.  Ask them what they would recommend for your project.  Oats, wheat, barley, and many others look similar to grass and if you collect the seeds you can replant them.  All of their roots are great for improving the soil, if that is necessary.  They may also have clover and other ground cover options.  Stop in to see what they have or see if they have a website.