Well lets see shock would probably show if the bird acts depressed, weak or lethargic, very rapid or shallow breathing These would be signs of stress, shock or sickness. Birds usually don't show many signs of sickness or shock though until they are at the stage they need immediate veterinary attention.
As far as CPR I could not even begin to guess. I believe any compressions of a birds chest would rupture it's lung (or air sac). Since the lung and air sac are not protected by ribs as a mammal's lungs are I think this would be impossible. Even picking up a bird by putting too much pressure on the chest area can result in death. Also as far as the breaths for a bird, a human mouth has so many toxins in it that are dangerous to a bird that it seems it would be more dangerous than doing nothing. If you are using a bag breather I am afraid it would be too powerful for even a larger bird and would again rupture. The best thing to do would be to use a steam vaporizer close enough to blow steam over the birds face but not so close it actually causes burn from the steam.
With a birds physical make up by the time it actually quits breathing it is probably too far gone for any real help. A vet might be able to open up the bird and massage the lung or inflate the air sac (not sure how likely or doable that is to be though) but only if it was in the vet office at the time it went into respiratory distress.
The only helpful hints I could give is that if you haven't already, study bird anatomy. This will show you better the positioning of the lung and air sacs. A birds lung is considered to be nonexpandable which again goes with the no real CPR for birds. I guess if the bird was in complete respiratory distress the very slight, gentle massage of the lung area with no pressure might start it to breathe again.
Sorry I couldn't be of more help nice to hear of your interest.
