You mean modulator.
The key to legality is checking with local and state/country laws. Strobes are usually illegal because they actually turn on and off quickly whereas modulators don't actually turn off, they only dim to give a pulsing effect. Even where legal, it is often illegal to use the modulator feature at night. It doesn't bother the rider as much as it really distracts drivers coming toward you.
If one isn't available for the VFR it's just wiring, you should be able to adapt one to work. Signal dynamics make a universal adapter that should work ok although I haven't tried it. It is out of stock though (Revzilla).