Writer, editor, irascible curmudgeon
I used to do a lot of work with essential oils and herbs. Based on that experience, I'd recommend that you not try to use the oils.
Essential oils are extemely potent. We used to have a problem with them melting the plastic caps on bottles. Unless you are planning on working with batches of tea in excess of 10 pounds, the problems with storage and tweaking the formula will probably outweigh the benefit. Cinnamon oil for example is EXTREMELY potent and a single drop will probably overwhelm a pound of tea.
Here's what I would recommend.
Get a couple of oranges from an organic supplier, (Commercial oranges are bleached with chlorine gas and dyed orange with a chemical dye.)
From the same supplier. get some cinnamon sticks.
With a vegetable peeler skin the zest (just the colored surface area of the orange peel) from the fruit. Avoid getting too much of the white pith which will make the tea bitter. If you do get too much, put the skin flat on the cutting board and scrape the white off with the edge of a knife.
Mince the zest finely, then spread it on a plate in a dry dark area to let it dry out.
When the orange peel is dry, it is time to experiment. Brew a cup of decaf black tea with a quarter tsp of orange zest and taste it. Tweak the amount until you get the orange flavor to your taste.
At this point, the easy solution would be to just pour the tea over a cinnamon stick, removing the stick when it gets to the required potency.
If you want to go all the way, though, crush the stick in a mortar and pestle or give it a couple of pulses in a blender or food processor. sift out the dust (it will look funky floating in the tea) and experiment with different quantities of cinnamon fragments in the tea and orange mixture.
It's a lot of work, but safer than messing around with esential oils.
You may be able to find a commercial supplier of dried orange peel.