I was on the search committee for my class, and I teach a beginning Internet class at our county library. The "Deep Web" is mostly for academics. If one of your classmates published a doctoral thesis, you might find him/her through it, but it isn't much good for your purposes.
Once in a while you can find someone with an exact phrase search in Google. That means you use quotation marks. You have to try all four forms of the name:
The case isn't important. You do have to use double quotes ("), not single ones (').
You might divide the list into fourths and share with three others, or into 10 parts if you can get 9 others to help.
Make sure the school secretary has a name, phone number, street address and e-mail address of a contact person.
Cobble up a web site or web page, even if it has to be Geocities or
Get the web keeper at Bentonville High to link to it.
For names other than Smith, Miller, Jones, call everyone in the town with that surname, explain why you are calling and ask if they know where "Mary Kowalski" has gone and what her married name is. (This is where many hands REALLY make light work.) If they know but don't want to tell, ask them to give her your name and number and see if she wants to call.
Finally, don't get your hopes up. Some people won't want to come or won't be able to come. We had about 150 out of a possible 500 show up to our 30th.
Here is some advice you didn't ask for that I paste every chance I get, hoping no one else will fall victim to the World's Stupidest Disk Jockey.
The most important thing you can do to insure a good time is talk to the DJ before hand. The people who never left town and see each other every week at PTA, soccer practice, poker night etc. are going to want to dance. The ones who DID leave town and flew 1,500 miles to attend are going to want to catch up, and they are not going to want to shout over the music.
The ideal solution, if you can afford it, is to hire two rooms. Unless you are from Beverly Hills High, you won't be able to do that. Having the music "on" for 30 minutes, then off for 30 would be a reasonable compromise. Promise the DJ the same amount of money as if he played all night. Impress upon him the desire of half the audience to talk. Reunions are not the same as dances or concerts. People don't go to concerts to talk. They do go to reunions want to talk. Keep hammering that home to the DJ. If necessary, tattoo it on his forehead backwards and give him a mirror. Appoint a "Quiet time" monitor.
Tell people at the start of the affair what you are doing, so they know. Tell them that you know half of them will be unhappy during the music and half will be unhappy during the quiet time, and you can't please everyone. If you like, you can tell the joke about the mathematician who had one foot in a bucket of ice water and the other in a bucket of boiling water. He said "If you take the average, I'm comfortable".
I hear "It was a nice reunion, but the DJ ruined it" a dozen times a year from friends and family.