Fungal infestations in tomatoes, as well as other plants, begins in the soil, infects the lowest leaves and transmits fungus spores upward through a gas that's released from the fungal growth. This is the reason it progresses upwards. The best cure is preventative... however, you sound like you're well beyond that stage. It may be to late to save your plants since, even if you affect a cure, the plants are under stress and not likely to produce much. Having said that, see if you can find
Daconil 2787, or
Ortho Multi-Purpose Fungicide... these have done well for me in controlling similar fungal growth in roses (they all tend to be about the same). Read this for preventative actions for next year:
http://www.hort.uconn.edu/Ipm/veg/htms/tomdis. htm
Best of luck!