There is almost no way that your son can play D1 baseball again.
If I understand your post correctly, he entered college in the fall of 2005, redshirted in spring 2006, played D1 in the springs of 2007 and 2008, and apparently is playing now in D2.
Assuming that he entered college full time in the fall of 2005, spring 2010 is last semester in which he can play any NCAA sport at the D1 level. That's because a player has 5 calendar years from the date of first full-time enrollment in which to compete. (14.2.1)
With one situation excepted, he can't compete next year (spring 2010) at a D1. The one-time transfer exception typically isn't available to baseball players (14.5.5.2.10), but in any case the transfer to another college would be the second transfer. The exceptional situation is the following: he could return to the original D1 school, and not have to sit a year, but only if he hasn't either competed or even practiced for more than 14 days at the D2. (14.5.5.2.8)
The Transfer Guide for which Ozone provided a link is very helpful. It doesn't cover every situation, and the
D1 Manual is better for looking for loopholes. Article 14.5 covers transfers.
