"You can't use adult organs because they are too big."
One solution might be to use organs from other species, if the problem of rejection can be overcome.
Under current rules, transplant centers get to use organs that are locally donated even if they could be better used elsewhere.
They certainly don't use organs from deceased cancer patients.
You did mention that you use infant organs in children's operations.
They have even used organs from 70-year-old adults in children.
Out of desperation, surgeons have also begun using less healthy organs.
They begin to fight in the morgue, using human organs as weapons.
Should transplant surgeons be using organs from nearly anyone?
Experiments using organs or cells from aborted fetuses began in the 1980's.