There are two Brachial arteries but only one Brachiocephalic artery in the body.
This is the diagram of branches of arch of aorta :
From the picture we can see arch of aorta has three branches : brachiocephalic artery, left common carotid artery and left subclavian artery.
The brachiocephalic artery is in right side and shortly after its commencement it gives rise to right common carotid artery and right subclavian artery.
Whereas in the left side, the left common carotid artery and the left subclavian artery arises directly from the arch of aorta. So, there is no left brachiocephalic artery. And we are left with only one brachiocephalic artery.
The right and left subclavian arteries then supply right and left arm by forming right and left axillary arteries. The axillary artery in each arm then gives rise to brachial artery. Yes there are two brachial arteries. One in each arm.
Here is a couple of pictures. First one shows how brachial artery is formed. The second one shows two brachial arteries :