DC Spoiler
I bought one on eBay from showcarsrob. Fiberglass reproduction of the DC spoiler with the standard cut outs for mounting with screws just like the DC version. He doesn't have any listed right now, but it seems like he is making them. He does say to contact him if you want anything other than what he has listed.
http://www.ebay.com/itm/1970-1976-Plymouth-Duster-Rear-Spoiler-/111458023881?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2047675.l2557&nma=true&si=7jAyiZ5sckZsGGuyFDAyC1W75FM%253D&orig_cvip=true&rt=nc
Honestly, I like the fiberglass version better than the original DC version. The DC version seems pretty flimsy, the ABS is pretty thin and I can see how it would crack. Especially around the mounting screws if you overtightened them. The one from showcarsrob will need a little finishing since its just in gelcoat, but its a decent piece. I'm going to try using plastidip on mine, I think the matte finish will look better than if I paint it to match the car.
There's another seller on eBay that sells a smooth version that mounts from underneath. He posts them on eBay somewhat frequently. Not every month, but at least every couple. Seems like the fiberglass versions usually end up around $200 after shipping, which is still less than what the original DC versions sell for if you can find one.