turns out they've made some versions available:http://airdroid.com/download.html
looks like this site is the best place to find most versions:
http://www.apktops.com/airdroid-1-0-9.html
http://www.apktops.com/airdroid-1-0-8.html
http://www.apktops.com/airdroid-1-0-7.html
http://www.apktops.com/airdroid-1-0-5.html
not sure about v1.0.6 and i had trouble finding v1.0.4 on there, but it's here:
http://apknew.com/airdroid-1-0-4-beta-apk.html
looks like this site is the best place to find most versions:
http://www.apktops.com/airdroid-1-0-9.html
http://www.apktops.com/airdroid-1-0-8.html
http://www.apktops.com/airdroid-1-0-7.html
http://www.apktops.com/airdroid-1-0-5.html
not sure about v1.0.6 and i had trouble finding v1.0.4 on there, but it's here:
http://apknew.com/airdroid-1-0-4-beta-apk.html