The 933 really is hard to find, isn't it. I see one for $19, but seller's feedback is only 98.4% positive. The "make offer" option is enabled. Might be risky, though? I'd at least check the details of recent feedback history. Maybe just typical high volume mistakes that are eventually made good?
The 867MHz module would be another option. Be careful when looking for that one, though. The QS had a single CPU 867 module and the MDD had a dual 867 module (QS and MDD modules are not interchangeable). Ebay sellers sometimes confuse Quicksilvers and MDDs. Look at the pictures.
The other OEM options would be the dual 800MHz and the dual 1GHz, but those are likely to be even more rare and more expensive. Also, the dual 1GHz is another one that sellers sometimes confuse with MDD modules.
The 867MHz module would be another option. Be careful when looking for that one, though. The QS had a single CPU 867 module and the MDD had a dual 867 module (QS and MDD modules are not interchangeable). Ebay sellers sometimes confuse Quicksilvers and MDDs. Look at the pictures.
The other OEM options would be the dual 800MHz and the dual 1GHz, but those are likely to be even more rare and more expensive. Also, the dual 1GHz is another one that sellers sometimes confuse with MDD modules.