I've used this in the past: http://www.xs4all.nl/~carlo17/howto/undelete_ext3.html

I've never used extundelete but it sounds like it is closely related to the link above if not a more maintained forked version of it.

The most important thing though would be to make sure that you stop writing anything to that filesystem.. preferably just umount instead of remount read-only before you do anything.

An EBS volume should just be able to be treated them same as any other block device so treat it like it it was directly plugged into your system and you should be fine. Are you sure you don't have any EBS snapshots? You might be able to attach one of those snapshots to your instance too.

Good luck. If ext3grep or extundelete don't get you your data then take a look at some file carvers to get as much information as you can. (I like foremost and scalpel, but there may be others out there that are better now)