You could try pushing a 400 speed film to 3200+ and develop via water bath... After a little practice, you can get your contrast where you want it.
I have also heard of some people developing film for a normal time (i.e. ISO400 time temp) and then inserting the film into a over-diluted developer for the remainder of the "pushing".
I have personally never tried this, after all one of the reasons I shoot large format is for a reduction in grain.
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