Hello Amit,
it is hard to choose alternate for MK20DX256VLH7 in K22 series, because there are differences with frequency and processor.
But if you find only processor, which will meet the conditions for 256KB and 64pin and will be from K22 series,
I have two candidates for you. Just for information you mentioned MK20DX256VLH7 - LQFP 64pin package, 256KB and 72 MHz.
MK22FN256VMP1 - there is MAPBGA 64pin package, 256KB, but different processor and 120MHz
MK22FN256VLH12 - there is LQFP 64pin package, 256KB, but different processor and 120MHz
I hope this helps,
Best Regards,
Iva