For an 8-bit ADC @ 10MSPS, that's of course 80 million/sec (76.3MB/sec) as flash writes in blocks, the chips usually contain a buffer you can fill up and 'block write' but not at that speed. You might be better off writing to ram, probably DRAM/SDRAM at that speed, and would require a bit of logic form a CPLD, or FPGA to set it up, don't think many microcontrollers would be up to that job. You could then dump that data onto the SD card after the ram is full.
As for 'real time', if this is for an oscilloscope, you could do what digital scopes do and thats take a burst of samples, at full sampling frequency, say 1024, into ram. Then stop and stream this to a PC, or, if you want, your card. That of course isn't going to be a continuous measurement, but its more practical, all depends on your application and what you wish to measure.