Supervolcanos have occurred in the recent geological past, but not within the past 74,000 years. Is it possible to find the magma chambers with no previous history of supervolcanic activity that are likely to produce supervolcanos?
I am a seismologist, not a volcanologist, but we can use a method called seismic tomography to understand the size of magma chambers.
This method is similar to a medical CT scan - the magma mush will have a slower seismic wavespeed than the surrounding 'normal' rock. Therefore, we can use this to determine the size of magma chambers from a tomographic image.
Even if a volcano does not appear to be active at the surface, it could still overlie a magmatic anomaly.
This approach was recently used to estimate the seismic of the Yellowstone magmatic body. See this paper: http://onlinelibrary.wiley.com/doi/10.1002/2014GL059588/abstract
Seismic tomography can theoretically be applied to any region, but we just need to have enough seismic sources nearby (e.g. earthquakes) to be able to do this accurately.
Complementing the answer by @seismo_steve, two other geophysical ways of detecting magma chambers are through their density and conductivity anomalies.
Seismic tomography is able to detect the chambers because they cause an anomaly in the propagation velocity of seismic waves. Likewise, the chambers cause an anomaly in the gravity field because their density is different from the surrounding/reference value. Geophysicists can use this gravity anomaly to estimate the size and shape of the magma chamber (see this paper by Chaves and Ussami, 2013, for an example also in Yellowstone).
Long-wavelength electromagnetic methods, like magnetotellurics, might also be able to detect the electrical conductivity anomaly associated with the magma chamber (though there are some restrictions). See this classic paper by Newman et al. (1985).