Easy way, there isn't really. The file hierarchy and way Apple saves out the files and proxies makes it hard to follow exactly where the originals are.
In Aperture they changed it so ( I'll assume because of LR proving a much more classic folder approach) so you can import from a normal file system and leave that structure intact, just as LR does.
How iPhoto does that I don't know.
Before you had to search for iPhoto library in your home/pictures folder, right click to show contents, look for your originals in the Originals folder . Then if you're lucky you can copy them to a normal file structure, import those into LR.
Problem with that is you'll loose any edits etc from your iPhoto library.
You could select all in your iPhoto library , then export all into a new folder with whatever settings you like , yet you won't be exporting raws.
Once you do what you have to , I'd dare say move away from iPhoto.
