Build your own Ares V
While plastic models aren't as popular during the new moon race as they were during the original one, there is still a sizable community of serious builders (including the real-space modelers, an under-represented segment of the hobby.) Kits of the next-generation spacecraft are being issued, albeit in small quantities and marketed towards serious hobbyists instead of the mass market. Realspace Models recently did a kit of the Ares I, and Fantastic Plastic has an Orion kit for sale.
Along similar lines, it is possible to build a 1/144 scale model of the Ares V, using mostly the components from existing Saturn V and Shuttle kits. The Saturn V models are produced by Airfix and Monogram, while the shuttle has been kitted by Revell, Airfix & Minicraft (formerly Entex.) For this project, I would recommend using the Monogram Saturn V and Revell Shuttle, because both kits are relatively easy to find, for very reasonable prices. The Monogram Saturn can be found on eBay, while the Revell Shuttle was recently re-released, and can be found at Hobby Lobby and local hobby shops.
Building the Ares V core
In studying the artists' concepts of Ares V, it appears that the Ares v core is almost as long as the Saturn V's first two stages, plus the interstage connecting the two. The diameter of the Saturn V and Ares V is the same, so this is a pretty easy part to fabricate. Simply glue the S-IC, interstage, and S-II together. The corrugated sections on the tube will probably need to be sanded off, because most of them are in different locations between the two rockets. The corrugations on the Monogram kit aren't very good to begin with. They can be replaced with corrugated plastic sheet, which can be found in the railroad section of well-stocked hobby shops. Several detail pieces from the Shuttle ET can also be used to detail the Ares V model, including the SRB attach struts and the LOX feed line.
The thrust structure and engines can be a bit of a problem.The Saturn V had a cylindrical aft end with fairings over the outer engines. While Ares V has engine fairings (albeit smaller ones,) the structure itself is tapered. While it might look passable to simply reuse the aft end of the Saturn V for this model (minus fins,) it would look more convincing to roll the taper and the fairings from thin plastic sheet. Finding a source for the RS-68 engines will also be tricky, but it might be possible to cut them down from the bigger F-1's on the Saturn V.
Stretching the SRB's
Using the standard SRB's from the shuttle kit, how can the 5-Segment SRB's be built? My solution is to cut the SRB where the nose cap meets the top of the upper segment. Then, using an Alumilite casting kit (or a suitable alternative,) make a mold of the upper segment and cast a new one in resin. With the fifth segment glued in place and the nose cap reattached, you've got a perfect 5-segment SRB (except for the new nozzle, which has yet to be revealed.)
Earth Departure Stage
Because the EDS is the same diameter as the shuttle ET, this will make the starting point of the model's upper stage. Remove the LOX tank and the aft dome from the tank with a razor saw. The corrugated portion of the ET will form the aft end of the EDS. If you're using the Revell shuttle's ET, remember to remove the incorrect raised bands on the surface of the ET.
Fabricating the bi-conic nose fairing of the EDS is tricky but not impossible. One solution is to take the LOX tank from the shuttle ET, glue it together, and reinforce the walls with epoxy. Mounting the piece on a lathe, it is possible to file it to the perfect biconvex shape.
The final details come from the Saturn V kit. The adapter between the Ares V core and EDS can be cut down from the adapter between the S-II and S-IVB. If the model is displayed with the stages apart (or if you make your EDS removable,) simply add a plastic bulkhead to the aft end of the EDS and use the J-2 from the Saturn V's S-IVB.
The project I've outlined above should only be attempted by the serious craftsman, and it's not for the feint of heart. It should also be remembered that the completed model is a depiction of Ares V as it appears in today's concept artwork, rather than a realistic model of what Ares V will look like in 2018. The real Ares V will undoubtedly change between now and when it finally flies, if it's ever built to begin with. If done well, the completed model will be a conversation piece and a majestic reminder of the Vision for Space Exploration.
By now, the only question is what should be done with the leftover pieces from this kit-bashing adventure. There should be a complete set of parts for a shuttle orbiter and S-IVB, sitting in their boxes. Perhaps a speculative model depicting the shuttle docking to Skylab should be your next project after finishing the Ares V!