Can I see any information about which machines are authorized against my iTunes account?
I also have the same problem and unfortunately there doesn't seem to be a way to view this kind of information at present. This is corroborated by several Apple Support Community threads here, here and here. 

As you say, the only option seems to be to either try to figure out which machines are currently authorized and deauthorize them using iTunes (particularly difficult in the case of multiple VM's or machines you no longer have) or deauthorize all and start again.