In my industry, (seagoing) many employers require physicals above and beyond what is required by the Coast Guard. Could it be possible that they found something disqualifying for this particular job? Many industries are physically demanding and the employers are keen to reduce potential workmen's comp claims. You may be healthy but if they saw something they were iffy about (and they really zoom in on back and knees), then there you go.
If the purpose of the physical was pre-screening, you probably signed something in that stack of paperwork they gave you that granted permission to release results to the employer.
If you can't get the results yourself, you might see if your own doctor can try...but nothing is guaranteed because they really don't have to send them to you.

