We have Omnimeters that are capable of metering electrical systems up to 480V, 3-phase 4-wire but unfortunately we do not currently carry meters that are appropriate for 600V systems. It's possible that you could use a voltage transformer or potential transformer, etc., to bring the voltage to a meter-able level. We do not carry these or have any specific product recommendations, however.
We are in the process of developing a meter that will be able to handle 600V systems. This will be available a ways down the road, however. If you would like us to let you know when we have this meter available, please send your request here: firstname.lastname@example.org