The place where syscall information is gathered is:

arch/alpha/include/uapi/asm/unistd.h
arch/arm/include/uapi/asm/unistd.h
arch/ia64/include/uapi/asm/unistd.h
arch/powerpc/include/uapi/asm/unistd.h
arch/s390/include/uapi/asm/unistd.h
arch/x86/syscalls/syscall_32.tbl
arch/x86/syscalls/syscall_64.tbl
include/uapi/asm-generic/unistd.h  (aarch64)

For src/ausearch-lookup.c:
Inspect include/linux/net.h for socketcall updates
Inspect include/linux/ipc.h for ipccall updates

For adding new arches, the following might be useful to get a first pass file:

cat unistd.h | grep '^#define __NR_' | tr -d ')' | tr 'NR+' ' ' | awk '{ printf "_S(%s, \"%s\")\n", $6, $3 }; '

it will still need hand editing