I'm an advisor for the chapter here and I'm not affiliated with an alumnae group. There is no alumnae group nearby. I say go ahead and fill out the volunteer form and send it in. I'm sure they would love to have your help. You sound very enthusiastic about your sorority. Your headquarters will know that there isn't a local alumnae chapter for you to be active with and they will probably be very understanding about it.
Also, have you thought about joining the Junior League? I've met a lot of great women through my JL involvement and while it is somewhat time-consuming at first, it's a great way to get involved in your community. Check out
www.ajli.org for more information.
Good luck!
PM me if you want to chat... I went alum in '98, so we're pretty close in age.