I see the file at support.arubanetworks.com
After logging in, I clicked on Download Software (3 tab along the top), then along the left ArubaOS, Standard Release, Current Release, Release 8.3 (I just picked one), Release 8.3.0.7, and then it is on the list ArubaOS_VMC_8.3.0.7_70587.ova
I hope this helps,