Is it the AROS-20110331-amiga-m68k-system/boot/aros.elf 1081644 bytes long that is the ROM image needed?
"file:"
AROS-20110331-amiga-m68k-system/boot/aros.elf: ELF 32-bit MSB relocatable, Motorola 68000, version 1 (SYSV), not stripped
The files you are looking for are in AROS-20110331-amiga-m68k-system/distfiles/
aros-amiga-m68k-rom.bin
aros-amiga-m68k-ext.bin