You will need to disassemble the gearcase completely to gain access to the Cam.
The cam is controlled by the shift shaft as it spins.
You need to remove the pinion gear and forward gear first. Take off the pinion nut, slide out the driveshaft and remove the pinion...followed by the forward gear.
There is a special tool required to remove the shift shaft retainer bolt at the top of the shift shaft on the gearcase.
Once its removed the shaft pulls out and allows the cam to be removed.
Some of these parts though NLA can still be obtained from dealers. Let me know if you need further assistance here
http://www.themarinedoctor.com/cgi-bin/YaBB.pl
The Marine Doctor