Doing find on / will search everything on your computer, including any mounted drives. To prevent this from happening, run:

find / -xdev -name bar.ova

By the way, you only need to run it with sudo if you ran the VBoxManage --export ... command with sudo. Otherwise, it's extremely unlikely that VBoxManage could have created a file somewhere you can't read from. You'll get plenty of "access denied" messages running find on / without sudo ...but that's not really a problem. If you want to log the results (but not error messages) to a file in your home directory, you can do this:

find / -xdev -name bar.ova | tee -a ~/find-results.log

If you have a separate partition for /home (which only happens if you set it up that way when you install Ubuntu, or deliberately migrate /home to a separate partition after installation), then find on / with -xdev won't search /home (which contains your home directory). The simplest and easiest solution to this is to do a separate find operation on /home:

find /home -xdev -name bar.ova

Or just on your home directory in /home, if you don't think you could've put it in another user's home directory:

find ~ -xdev -name bar.ova

You may want to leave off -xdev in these cases, though it's possible you (or other users) have FUSE or GVFS shares mounted inside home directories. (It's also possible a file got saved into one of those shares...)

With -xdev, when running find on /, it will still take a while, but it will complete eventually.

Something else you may want to try is to run sudo updatedb, wait for that to finish, and then run locate bar.ova.