i got my black lab to find sheds basically the same way i trained her to find birds. She found the first shed of the year this year.
I started by throwing a 2 point shed in the yard just like a ball. I would have her retrieve it and praise her when she brought it back. I did this for a couple of weeks untill she started carrying it around with her for me to throw.
I then took her in the house and would have her sit and stay while she watched me walk into another room. I would place the shed in the middle of the room..walk back to her..give her the command and have her run in and grab it to bring it back.
it took 1 try for her to get that down. so i would do the same process but would hide the shed in a blanket or on the couch. She would scower the room till she found the shed.
I then (still do this) would take her out to my dads land. I would hide 4 or 5 sheds while she sat in the truck at a point she could not see me. I would walk her in the general area of each shed giving her ample time to work around for each shed.
I will also note that i stopped letting her bring me sticks. She can only retrieve a ball or shed for me(except for bird season of course). She finds more sheds then me now.