Quite a lot, but hard to estimate. There are perhaps 500 billion stars in the Milky Way, of which something like 0.002 G-type stars with the same luminosity as the sun, per cubic parsec. There are about 0.13 stars/cubic parsec in total, so that sun-like stars are about 1.5 percent of the total population, which makes for about 7 billion stars like our sun in spectral class and brightness by my estimates.