Unfortunately, there are no parts, except from another Tek attenuator. Is it blown, or are the contacts "dirty"? These were often damaged by DC or excessive input power. If it is damaged, you need to check the first mixer for damage as well. You may be able to find a good attenuator on eBay, perhaps elsewhere, but these can be difficult to find in good condition.
It is possible to disassemble these and make one good unit out of two. The thin film resistive elements can also be inspected. Usually the damage is readily apparent under magnification.
It would be possible to fit a different attenuator, with the correct steps, and frequency range, altering the drive signals as required.
Be sure to take anti static precautions around the mixer.
Good Luck,
