Hi,
If you've purchased it from the Mac App store, you should be able to
redownload it. When it opens the installer, go find it in your downloads
or applications folder (I think it's in the latter place) and make a copy
of it. Then you can either quit the installer or go ahead and install.
If you've not bought it on the mac app store and you can't find it there
anymore, see if anyone you know can do the above. Then they could use
something like Lion Disk Maker http://blog.gete.net/lion-diskmaker-us/
We have done this a couple of times.
Geoff.
