Publicly accessible database for the Autistic brain under MRI and/or fMRI
I'm not personally familiar with this project (outside my area of research), but a quick search brought me to the Autism Brain Imaging Data Exchange (ABIDE):

http://fcon_1000.projects.nitrc.org/indi/abide/

Based on citation counts for the primary articles, it seems popular. If you want to compare to other types of brains you will probably need to use multiple data sets and combine them.



Di Martino, A., Yan, C. G., Li, Q., Denio, E., Castellanos, F. X., Alaerts, K., ... &amp; Deen, B. (2014). The autism brain imaging data exchange: towards a large-scale evaluation of the intrinsic brain architecture in autism. Molecular psychiatry, 19(6), 659. doi: 10.1038/mp.2013.78.

Di Martino, A., O’connor, D., Chen, B., Alaerts, K., Anderson, J. S., Assaf, M., ... &amp; Blanken, L. M. (2017). Enhancing studies of the connectome in autism using the autism brain imaging data exchange II. Scientific data, 4, 170010. doi: 10.1038/sdata.2017.10.