Does anyone sell dragons scales or bones?

No, no one sells them, but you will continue to encounter dragons after the main quest line so you won't run out of bones

No

Dragon Bones and Dragon Scales are not sold by any vendor.

After you've finished the main quest, the random dragon encounters still happen

and you can now call upon Odahviing to help you fight those dragons

You can still get Dragon Bones and Dragon Scales as well as Dragon Souls from those Dragons.

This'll allow you to create all the dragon armour you want, as well as unlocking all the available shouts.

No, there aren't any dragon bone/scale sellers.

What you might want to do is go to those places where you are sure to find dragons. If you are low level, change the difficulty to novice. Each dragon gives 1-3 dragon bones and scales, no matter what type of dragon it is.