I mean, You can buy the fruit yourself, eat it and plant the seeds.

I understand that you might want to have cetain type that you cannot buy on the store but still they look really similar. As we know a seedling will take years to flower (if it will ever flower)

Welcome to the Citrus Growers Forum. We are glad to have you as a member. All citrus grown from seed will flower and fruit when the tree becomes mature. Depending on the variety of citrus seed that was planted the wait time until fruit can be as short as 2 years, many at 5 years and as long as 8-10 years. - Millet

Millet is correct. Also, it depends on the conditions grown, cultivar, your climate, crop management, etc. So it could range from 18 months to 25 years or even more.

The main reasons why they buy seeds instead of fruits is that seeds are easier to ship or carry with you than fruits. Also, most countries allow importation of properly treated seeds than fruits, the case of USA for example. But the fruits are the best way to carry the seeds, the germination rate would be the best if you buy the fruits.

Here in England its a pain getting hold of some fruit. I have wanted key limes since February. I thankfully just traded with someone and got 25 seeds. I planted them a week ago in a heated propagator and 7 of them are already growing out of the soil. So sometimes it can be due to not having the fruit available to buy.

Some others also enjoy growing seeds. I love growing them - there is something satisfying about nurturing a plant from seed to maturity if you are patient enough. I have the key lime seedlings which will take a couple of years to flower. I also have others, including a grapefruit. By no means do I expect to get a fruiting tree while it is containerized, but it is for the love of growing from seed that it was planted.