First off...I have no problem with 6th or 7th rounders being rated in the low 70 range. Tom Brady anyone? (6th round pick)
I'm not sure what the formula is for what a rating in NCAA equals to in Madden, but what I do know is that it really kind of decreases the talent gap in a lot of players....which is fine and again, pretty realistic.
As for where to download Madden Draft Classes...you don't have to look very far....check out the Madden Rosters section of this very message board for 5 years worth of draft classes.