There are dozens and dozens of reliable seed banks and breeders available to us online these days. Most of them are legit in the sense that you'll make a payment and receive your beans, but trust me when I tell you the quality of the genetics varies wildly from breeder to breeder. You really want to avoid the huge white label seed distributors like ILGM, Seedsman, Royal Queen, Crop King, Blimburn and Growers Choice. They all just outsource their seed production to massive farms and then slap a popular name on the label like Sour Diesel or Blue Dream. Unfortunately there are many inexperienced growers who don't know any better so they buy these seeds not realizing that what they are getting is not actually the real Sour Diesel or Blue Dream. If you ever see a seed bank selling all the super famous and well known strains like Ice Cream Cake, Sour D, Chemdawg, Blue Dream, G13, Skunk #1 etc etc then you can be certain that they are just another deceitful white label distributor. I always suggest you avoid the big Dutch banks/breeders like Greenhouse, Dutch Passion and Sensi. They have all gone really downhill over the last decade (or so i've been told).
You want to order seeds from actual breeders. Many of them sell direct to consumers but some only sell their genetics through seed banks. I prefer to order directly from breeders when I can because they're often cheaper than ordering from banks (middle men) and the freebies are usually better. With certain breeders that is impossible, though, so ordering through a bank becomes necessary.
Some of the top seed banks are North Atlantic Seed Co, Multiverse Beans, Deeply Rooted, Breeders Direct Seed Co, Great Lakes Genetics, JBC Seeds, Revolution Seeds USA, Black Dog Seed Reserve, Terpy Seeds, Silverstar Seed Bank and Horror Seeds. There are others but those are some of the best imo
As far as quality breeders who sell direct to consumers go I highly recommend checking out Raw Genetics, Bloom Seed Co, CSI Humboldt, Tiki Madman, Clearwater Genetics, Atlas Seed and Greenpoint Seeds.
Other breeders who you should look into are Bodhi, Wyeast, Symbiotic, Solfire, Top Dawg, Detroit Seed Co, THC Titan (Square One & Robinhood Seeds), Sin City, Black Hawk Genetics, Reverse Genetics, Purple Caper, Wolfpack Selections, Lovin In Her Eyes, Humboldt Seed Co, Grow More Fire, Blockhead Buds, The Honey Sticks, 3rd Coast, Right Hemisphere and In House Genetics.