Unless you're buying from like, amazon or something, there are a lot of great online nurseries these days. A little googling about the nursery or the "about" page should give you a good idea if they're "sketch" or not. Generally, if an online seed seller is legit, they should tell you where they are based, and a little something about their growing methods/style. They should also try to sell you plants that will thrive where you live, and will have easy to-access information on growing zone, days to germination and harvest, and details like heirloom status, deer-resistance or pest resistance.
Outside Pride is generally a pretty legitimate source for seeds, but I don't know how well ajuga in particular germinates from seed. I do, however, know that it spread quite robustly from rhizomes. Anyone who has some will, likely, have plenty to share, because it does not like to stop. It may be worth checking a local "free" site, or a trusted local nursery. You don't need a lot of plants to fill a truly huge space.