There may have been some made in the past, and some manufacturers have built a fan into their VRM heatsinks, but the wide variety of VRM configurations makes it hard to market a fan that will fit all models. So it's not done very much, and ones you do find won't likely work as expected.
The cheapest and most common strategy has been to zip-tie a fan to something...like the rear case fan or even the CPU heatsink...so you can orient it in the direction of the VRM heatsink. If the heatsink is well enough finned it doesn't have to be a large fan (even a 50mm can make a big difference) since the idea is to move air out of the dead-air zone common in that part of the motherboard. You have to be sort of creative about how to do this
You might also get a fan L-bracket
like this and be creative about where to mount it along with a fan to blow across the VRM heatsinks. Remember you can cut off excess length to make it fit, and screw it to one of the unused mounting holes on a rear/top case fan and then rotate the bracket (and fan) about that axis to point it where you want.
Something I've done is put a fan on the output side (at the rear, exhausting to the rear case fan) of a tower CPU cooler if you're using one. Normally air flowing out of the fin stack is laminar flow, so it goes straight to the exhaust fan, creating the dead air zone under the exhaust fan where a VRM heatsink is usually located. But the output of that fan will be highly turbulent and moves the hot air out of the dead zone which cools the VRM very effectively.
Probably more an act of desperation is to leave off the cover plate for the I/O connections. That open space lets you put a fan outside the case blowing hard right into the area of the VRM to cool it. It seems desperate to me, but some have reported it works well.