Grec said:
Hopefully we get to see it in Lonesome Road, but if it's not in there I'm gonna cry on the floor and cut myself.
It'd probably be less painful to download the GECK and make one yourself, if only slightly.
To me, a crossbow never quite felt like it fit the setting, especially when one takes the long view and considers the series' themes and influences all the way back to the first game. They seem to have steered tribal weapons development away from anything more complex than thrown projectiles, whether to underscore the tribes' primitive natures or to avoid accusations of aping or parodying Native American cultures. On the other end of the spectrum, you've got the "civilized" folk, who've already made the gradual climb back up from scavenging the old world for guns to manufacturing their own. Neither social strata really had call to put the effort into re-inventing or re-popularizing the crossbow. Historically speaking, it was kind of a half-step between classical bows and rifles, anyway, and this is a setting where rifles are readily accessible.
It doesn't seem that it would be something that would really even
occur to people to build, especially a people descended from "world of tomorrow" first-worlders, and for the same reasons you probably wouldn't find 'em just laying around in pre-war ruins. Even in real life, they're exclusively a niche weapon, possessed mainly by period re-enactors, "I wanna be able to say I've killed one of everything
with one of everything" Ted Nugent-types, and the sort of junior high-schoolers that buy mass-produced chinatown weaponry from the same dank hobby shops where they get their Magic the Gathering cards and 20 oz. Mountain Dews.
(If you really want a crossbow, though, the dart gun from FO3 comes pretty close for most intents and purposes, and I'm sure there's already a mod on the Nexus to get it into NV.)
(While we're on the subject, though, it never did fully make sense to me that tribals never got around to re-discovering traditional bows-and-arrows, or slings at the very least.)