there are many vehicles that use the qr25, maybe something from altima or frontier? they should be the same bearings as long as theyre from the qr25. maybe nissan forgot to list them for the ser? try asking the guys over at b15u.com, they usually have parts numbers everywhere.
after looking at my fsm, its saying to check the clearences using the cam brackets. when it is out of spec, says to replace cam and head since theyre machined together, lol.