There aren't any suppliers on this website - if you're looking at anything to do with plants available to buy, they'll be advertisements with no connection to this site.

If you want an apple tree, you need to think about which variety and what rootstock you want (dwarf, semi dwarf and so on) and a suitable pollination partner. I'd recommend having a look at Keepers Nurseries website, they specialise in fruit trees, have a lot of info on their site and are helpful on the phone.

Keepers Nurseries, Frank Mattews or Blackmoor Nurseries supply quality trees or go and view them at your local nursery. After a bit of swatting up, remember that the older the trees, then the quicker they will fruit. So if you want a crop, sooner rather than later, then a pot-grown will do the trick (rather than a bare root maiden). But the downside is, they will be a lot more expensive. Just as an aside, it will help if you can find out which varieties do best in you location.

And remember you'll need two if you want fruit, that will flower at the same time.

From seed, an apple tree can take anywhere from 5-7 years to bear fruit and the first couple crops ain't nothing to brag about. It needs a couple tries to figure out how to make apples. Variety, environment and husbandry have everything to do with it too. As Jimmy says, just find a reliable supplier-then you won't have to worry about root stock, blah blah blah. Your tree will be ready to start producing fruit. Just take the time and effort to learn 'Best Practices' for cultivating an apple tree to maximize fruit production. I invite you to look through my apple blog. Notice how the trees are loaded down with fruit that is within arm's reach - no climbing ladders. This is what you want. My favorite apple? - Golden Delicious! Other greats are 'Honeycrisp' and 'Cinnamon Spice Apples'. Depends what you like and what can grow in your location. Let your supplier guide you.

Here's the link to my Apple Blog.
https://growsonyou.com/bathgate/blog/29118-apple-blog