On the contrary, finding the wavelength of a large object is quite simple:
wavelength = h/momentum
, where h is Planck's constant. The wavelength of a .5kg beach ball going at 1 m/s, for example, would be 1.32x10-33 m-- less than a million million million millionth of the diameter of a hydrogen atom. A wavelength found in this way is called the de Broglie wavelength, named after Louis de Broglie, the French physicist who derived this formula and won the Nobel Prize for physics for his efforts.