While this isn't shrink-wrapped it looks in good condition.
http://www.ebay.com/itm/Marathon-Trilogy-Mac-Computer-Game-BUNGIE-/120831108328?pt=LH_DefaultDomain_0&hash=item1c221864e8#ht_500wt_1353
Opening bid is US $25. Maybe worth it for the Marathon Scrapbook and the 2nd CD loaded with 3rd party stuff which is becoming increasingly difficult to find on the net these days.
The pic on eBay shows the contents which appears to include a Marathon manual. I don't recall that in my box set.
Cheers
Hamish