The Toy Expo doesn't need any more volunteers at this point, as its much smaller than C4, but C4 itself can use all the volunteers it gets.
info@c4con.com is the email I think.
I stepped down as a co-ordinator after last year so I'm not that in the loop with their general organization at this point.
www.c4con.com has all the info you would need.
The best way to support the March show is to come out and buy a ticket to get in! I hope to see you there.