LMX1204: Recommend an input clock chip compatible with LMX1204(LMX1205)

I am considering using LMX1204 or LMX1205 in a project with synchronization and phase requirements. The clock frequency range for four synchronous outputs is 2.8G~6.4G. As LMX1204 or LMX1205 does not have a VCO internally, an external clock signal is required. Can you recommend one.