As far as finding an OE XL600 cam goes your up the creek without a paddle. I just checked E-Bay England and Germany. No cams there either. Your only option is a Mega Cycle regrind/repair.
BTW...They will not warranty the cam unless you do the rockers also. By the time all is said and done it's $500.00 for the cam and rockers. BTDT
Steve in SF
87 Harley FXRS-SP ~ 06 KTM 625 SMC ~ 72 Honda CB750/915cc ~ 92 XR600/654cc ~ 95 XR650l/675cc ~ 03 CRF450r ~ 05 CRF450x ~ 02 XR650l/675cc ~ 86 YZ490 ~ 93 YZ80 ~ 93 XR650l Project