For the past 15 years, I’ve been a loyal customer of Adagio Teas. 
Adagio has enabled me to become somewhat of a tea connoisseur, in that they tell you not only what country your tea is from, but (usually) which estate, the time of year it was picked, how many leaves were picked from each branch, how it was processed, and more.
I also love how they share stories of the actual workers and farmers who harvest and process the tea and that they buy straight from the origin, not through middlemen.
Add that to outstanding 
customer service, and it’s a huge “win” all round.
Here is the formula for my own custom blend:
8 parts Darjeeling Rhapsody No. 22 (aka Darjeeling Sungma Summer)*
4 parts Assam Harmony*
2 parts Ceylon Sonata*
1 part Keemun Encore*
Brewed up in Adagio’s IngenuiTEA Pot, it’s DE-lish!
And even though my blend is made of top-quality gourmet tea, each cup costs only about 25 cents!
If you’re looking for a tea supplier, you can do no better than Adagio.
* (The lovely tea images above are from Adagio’s site!)