With the high water we had last season, there may be a few more options. But yeah, Travertine falls... which is below travertine grotto, is a good camp. There is potential between mile 241-243ish. there were some good beaches in there, but I don't know what it will look like this year. Spencer canyon (246) has a good camp, but watch out for Hualapai trips coming through around midday. They'll come in and use that space even if you're there. They don't camp there, they just use it for a lunch stop and they have installed a composting toilet there. Below that, Surprise canyon should have some sort of camp. After the 2008 high flows, there was an awesome sand bar below the main camp. The main camp is great, but the parking is shallow, so watch out with the fluctuating flows. Other than that, it's hard to say. Some groups that do Diamond Down trips have made a few camps in silt flats hell. I feel like I saw one last season developing somewhere above Quartermaster Canyon on the right. I believe it's at Burnt Springs Canyon around mile 260... right above the Hualapai docks and heli-craziness. But it's not in view of all that. Maybe something around Salt Creek, just above mile 256, but I don't quite remember. We never camp down there, we're always on our way out, so I'm sorry I can't give you better details on those two.
Otherwise, I've used a camp just below mile 273. It's on the inside of a left hand corner. The river pinches up agains the wall on the right, and there's a small pull in for a decent sized camp. Groups have been using it on Diamond Down trips, and developing it a little bit. Be careful, if you aren't tight to the inside of that left hand turn, you'll miss it. It appears out of the willows at the last second. There are two places to pull in. One is a small opening in the willows, that seems better suited for a groover spot (and that is indeed what we've used it for). That spot you can actually see from a little ways upstream, so if in doubt, land here and scout the rest of camp and the other pull in. If you land there, look for a trail through the willows and follow it until you find a bigger pull in. There is room for 6 boats or so. It's actually a great camp I think, even if you have to be a bit creative.
Hope that helps, even if some of the info is sketchy and not entirely up to date.