you could probably do multiple installs of joomla with k2 in subdomains to accomplish this, but
wouldnt there be the same number of categories and subcategories either way....?
For the us i would create 50 categoires, then under each of them i would create a few categoies with the same name under each of the 50
if you use multiple installs you will encounter multiple databases, extensions, plugins, upgrades, etc etc all more work