You can get a Transmute Diamond recipe from the crafter in Marleybone. It allows you to change 15 ore into 1 diamond. So go around collecting Ore, Dragonspyre is a good spot. You can always get a few in the Athenium, then change realms and look again.
Diamonds come from ore all around Dragonspyre. They can also be crafted but you will need a lot of ore for it. I believe you can learn the diamond recipe from Felicia Worthington in Marleybone. Hope this helped :)
Diamonds can be found in the Bazaar. Unfortunately, it's a bit scarce there, but if you sit and 'farm' the Bazaar for a bit, you can actually get quite a few diamonds. There are also plants that can give you diamonds when harvesting or at elder (check the wiki at W101 Central). I do believe that when you collect ore (I think it's ore) around the spiral, you have a chance at getting diamonds as well.
Diamonds can be picked up along with other regeants (like how sometimes you get acorns when you pic up mist wood); the most common collect it's with, I think is stone blocks. They could probably also be picked up with ore, but I forget. Hope this helps.