In the Chicago area there's
Niles Animal Hospital & Bird Medical Center, which many people swear by, and
Glenwood Village Pet Hospital - Glenwood, IL, which is the vet I see. Take the dead bird in a small box to the vet and ask for a necropsy, that will attempt to find the cause of death. Bring the live bird in a small travel cage, he should have a checkup.
I highly doubt it was falling off his perch that killed him. If he was healthy, he would have been fine. There is any number of things that could have killed your bird. It could even be an illness that could spread to your living bird. That's why it's so vital to get the living one to the vet. It's also why you should take your bird to the vet regularly, so they can catch any signs of illness. I don't mean to be insensitive, but there is a possibility that if you had taken them to the vet the bird wouldn't have died.