"take duplicolor's line of paint which includes primer, primer sealer, topcoat, and reducers (hardners) which is the line of paint i used on the 71 midnight blue beetle in the pics reciently, and that was sprayed on."

Reducer and hardener/activator are not the same thing. If you used extra reducer thinking it was also a hardener, that's why it took 3 months to dry.

What's the part number of this
all-in-one reducer/hardener?
To my knowledge, Duplicolor does not have a hardener at all? The hardener/activator has to be sourced from another supplier which is why I recommended Omni. If I have that wrong, set me straight.