If you're Horde then just hit the Org side starting area - you'll slaughter the bugs at will at 80 and while they dont have a spectacular drop rate for the chitin, the respawns are so fast that you'll easily make up for that.
Plan B would be the bugs out near the Argent camp starting area - wont die quite as fast and easy but since they're higher level you'll be getting real leather instead of scraps and the area is big enough with a fast enough spawn rate that you should still be fine.
Plan C would be the caves that lead into the two bug heavy instances - populations and spawn rates are ok but unlike the other two, the bugs are spread out and there's a lot of traffic through the caves meaning that there's going to be intentional and unintentional competition.