Does anyone know any math/stat/operations research grad schools accepting students for PhD in math/stat or MS in financial engr/operations research in the spring semester?
I don't know of any programs that specifically start in the spring, but many will be willing to consider admitting you in the spring if they still have funding left. This would be on a case-by-case basis. Try contacting a few programs you're interested in and seeing if they would be willing to consider a spring admission - I managed to convince my current grad school to take me in in Jan because I applied very late.