Formulated seed mixes from feed stores seem to be the best bet, though they tend to come in sizes twenty pounds and over. I'm currently not well versed enough to mix my own seed mixes, though that's something I'm working on researching. Everything tends to be focused on racing pigeons when I just need a good ol' maintenance blend since my pigeons are just pets.
You can potentially find smaller bags of proper pigeon and dove mixes at specialty bird farms, but there are also brands at Petco and Petsmart. The latter (just Petsmart's brand) I don't really like, because their mix is for wild birds so I guess that gives them license to be nasty and filled with more dust and debris than I care to give my birds. The former will have a Kaytee dove mix that I've used before with success; it's a mix of predominantly millet, milo, I think some safflower, and peas (though my ringnecks wouldn't touch the peas) and some pellets. The ingredients are a bit difficult for me to parse, since it doesn't list the seeds separately from the pellet's ingredients so it's just kind of a mess.
As for pellets, you can get those from feed stores, as well, but make sure you watch the amount of protein. I try to aim for less than 15% for my guys, but a lot of pellets formulated specifically for pigeons get up into the low twenty ranges which is too much, I think, if you're not racing or free flying your guys. Chicken pellets are good for supplementation, I'd just be sure to watch the salt content, chickens need more salt than pigeons do. However, I've heard anecdotally that pigeons can do really well with chicken pellets added to their seed mixes.
Sorry if a lot of that is vague and anecdotal ha, I still have plenty of learning to do! I have a few sites stored away somewhere that goes into more detail regarding the nutritional value of specific seeds and grains, and I know some folks who keep pigeons just as pets so I can ask around and see what kind of formulation they feed if you have more questions!