"Contrary to common opinion" most old lenses were not soft. Look at any old daguerrotype with a strong loupe, and you'll find it to be sharper than any modern film!

But all is not lost: Portrait lenses and faster Rapid Rectilinears (and Aplanats) have a very limited sharp coverage at full aperture, maybe 15 to 30. The center sharpness rivals any modern lens (and outperforms most), but the sharpness drops off rapidly and dramatically towards the edges. Using a RR or Aplanat in about the same focal length as the film diagonal (like a 6" on 4x5") will get you "authentic" softness for around $15.