Read Thyristor(Triac) specification
Your varistor is BTA06-600CW.

Look for BTA06 and number behind dash at least 600 (this is blocking voltage, so 800 is even better) :)

Also CW is important as it means 35mA snuberless, it may be important depending of the actual circuit.

datasheet

EDIT:
Or simple:
Buy either BTA06-600CW or BTA06-800CW