Starship Asterisk*

I'm working on a fairly strange problem. I'm trying to figure out the apparent magnitude of about 130 minor planets (asteroids). This is an easy problem thanks to NASA (http://ssd.jpl.nasa.gov/sbdb.cgi), however, I need the apparent magnitudes on the specific dates that they were discovered (e.g., Sept. 1, 1850). Any idea if there exist formulas/simulations/online calculators that can do this?

Thanks in advance!