The 2nd edition of 3rd grade is not actually all that old. I bought it for my (then) youngest a few years ago. It's not like the ancient 2nd editions of the upper grades (4-6). BJU must have gotten out of whack in their updating, somehow.
Oh, and I have it, if you want it! :) Super cheap, just for you!
And I just checked, and it's the version they are still using for distance learning. I wonder if they just mainly rearranged it for the newest version, after the other elementary levels were out - that's awfully close between editions, and it was towards the beginning of the revisions, IIRC.
http://www.bjupresshomeschool.com/webapp/wcs/stores/servlet/product_Science%203%20Student%20Text%20%20Distance%20learning%20only_10151_-1_11201_1508954