You would need to find the passenger grab rail plus the rest of the hardware to secure the rear turn signals to the mounting tab:
84101-341-700 (grab rail)
33604-323-670
33605-323-670
33606-074-010 (two req'd, one for each side)
80108-061-010 (two req'd, one for each side)
93700-06025-0B (two req'd, one for each side)
The turn signal stems appear to be intact. The part numbers above are for a 1974 CB750, the part numbers for your motorcycle may be different, since the resident psychic is on sabbatical and you failed to include any information about what motorcycle you are referring to....
partial credit for the sticker in the photo that at least identifies it as a 750...