As a scientist, I guess, you'd prefer to know its crystal structure, because then you can calculate with free software the diffraction pattern by yourself. NaCl structure, Fm-3m, lattice parameter 4.178 Angstrom. At ambient temperture NiO is in fact antiferromagnetically ordered which induces some slight rhombohedral distortion, which is however (I think) not easily visible in ordindary powder diffractiond data.
You can download "MERCURY" software (https://www.ccdc.cam.ac.uk/solutions/csd-system/components/mercury/), and go on COD (Crystal Open Database) to find lots of XRD patterns!