What sensors can measure 3-axis acceleration?
The acceleration sensor i found was sensors that measured the gravity on 3-axis of the sensor


Gravity is acceleration.

An accelerometer measures acceleration - or more accurately, it senses the resistance to acceleration (inertia) and equates that to acceleration.

By holding an accelerometer still you are causing it to resist the pull of gravity, and it's that "resistance" that it measures - a constant 9.8m/s²

If you let the accelerometer freefall it won't be resisting gravity any more, and will measure 0 for the Z axis.

So you simply have to "ignore" gravity, by removing that constant 9.8m/s² ("1g") of acceleration from the Z axis.  And you do that by simply subtracting it.

It is normal to calibrate an accelerometer by keeping it at rest and reading the "idle" values. Those values are then subtracted from the readings to give you the actual value.