Hi Sam.
If you do not have XMODEM or TFTPDNLD command available then your only option might be to use another router of the same model (NPE300) and make a set of new flash devices ready in that one and then move them to your faulty one.
I do not have access to a C7206 NPE300 so I can't verigy, but aren't here any commands to do a download to flash when you are in ROMMON - perhaps just named in another fashion?
HTH, Ingolf