https://www.google.ch/search?q=33321-60029&client=ubuntu&hs=n7l&channel=fs&source=lnms&tbm=isch&sa=X&ved=0CAgQ_AUoAmoVChMIzfe61_3yyAIVQdkUCh11wwOC&biw=1024&bih=60733321-60029 seems to be the standard HP/Agilent RF attenuator type. Used all across their RF/microwave instruments.
You can screw apart both end caps, then you can slide away the metal cage. Then you'll see 3 or 4 electromagnets that operate tiny metal spring contacts in the upper section. That upper section is screwed shut with lots of screws, but you can take it apart without breaking anything. You have to remove the plate on top by unscrewing those 2 nuts on SMA connectors to before you see those screws.
Then you'll see those tiny gold plated metal spring contacts. On the part you screwed apart are 3 or 4 tiny ceramic or sapphire plates with dual Pi-attenuator elements (30dB/40dB elements are stacked Pi elements)
Even those ceramic/sapphire plates are sometimes cross compatible between instruments. I know that because I exchanged the 10dB and 20dB attenuator plate in one of my cheaply acquired 8566B that some previous owner had toasted with overload.
Because I didn't have money to buy new old one from ebay for 275$ (almost as expensive as the complete 8566B), I started to look in my trashed instruments. HP 8657B (in which battery has exploded) has dual 3 element attenuators (but with non compatible attenuation factors). I found good elements in 8672A attenuator (also bought cheaply, but YIG was dead, so parts unit for me). It has 1x10dB, 1x20dB and 2x 30 or 40dB elements. So I took 10dB and 20dB plate and 8566B was working like new.
The ones for HP-8657B have parts number 33321SC and 33321SD. If you take picture of your attenuator top section (attenuator elements), you can see what attenuator elements it uses. That's important, because 30/40dB elements are longer than 20dB element which is also longer than 10dB element.
If you took pictures of yours, I'll take pictures of my 33321SC and 33321SD so you can see whether they are compatible. Then you can buy cheap 8657 attenuator.