You could try and copy of the images from the working switches. (TFTP) But the boot monitor is very basic not sure it will support IP to copy up the image.
Not sure if Nortel do a binary image for the 5510, if they do you might be able to image it over a serial cable and using hyperterminal make the bin image available. I had to do this on a WSM a few years ago. It takes a long time to copy the image. Instructions if this is possible will be on the Nortel site.
Regards,
Mat.