I used this as my justification for adding Imperial Scepters to Paradise.
Emperor Vladimir Alecto created and distributed 40 Elector Rods to the 10 Royal Houses, the Church and the League. Where are they all today?
Initial Distribution
Initially, one imagines that Vladimir gave them out equally to the Royal Houses, 3 to each of the Ten, and then 5 each to the League and the Church. That sets up an initial distribution:
House Alecto: 3
House al-Malik: 3
House Decados: 3
House Gesar: 3
House Hawkwood: 3
The Hazat: 3
House Justinian: 3
House Li Halan: 3
House Van Gelder: 3
House Windsor: 3
Church: 5
League: 5
We know today that there are only 35 Elector Rods -- five have been lost - and that the League, at least, still possesses only five. (MotJW 16)
Extinct Houses
One of the five lost rods can be accounted for through House Alecto; we know that at a vote scepter was destroyed when Vladimir's flagship crashed into the sun. (S&R 116) One of Alecto's other two rods might have gone to the Hazat; the Alecto controlled land on what are now the Hazat worlds, and we're told that the Hazat were the primary aggressors and inheritors of House Alecto's wealth, though they were unable to capitalize upon their acquisitions. (LotKW 53) Alecto's last rod may have simply been lost in the fighting over the house's remnants or may have been destroyed, as we're told that one other scepter besides Vladimir's is thought to have been destroyed entirely.
Much of House Windsor was absorbed by House Hawkwood (LotKW 18) -- it's not unreasonable to believe that the Hawkwood inherited the Windsor scepters, too.
We know very little about House Gesar, and so it is perhaps convenient to name the Gesar as the source of the three still-unaccounted for rods. The Gesar met their end on Byzantium Secundus; hub of intrigue that it is, their rods may have been seized by secret societies, smuggled to a Lost World by Gesar loyalists or just have disappeared into the maze of the throneworld's enormous cities. It is also possible that Gesar's rods were seized by other houses who lost their rods in similar situations -- Justinian could have seized a Gesar rod, for instance, only to have that rod disappear when their home planet of Paradise became a lost world.
Fallen Houses
Two former Royal Houses are now minor houses, and no minor houses still possess elector rods. In the case of House Van Gelder, it is easy to imagine that they gave House Decados their scepters when the latter house brought the Van Gelders into the fold.
Finally, we are explicitly told that House Justinian traded its elector rods to the Church in exchange for protection. (LotKW 106)
Distribution Today
With those explanations, the present distribution of elector rods is as follows:
Church: 8
League: 5
House Hawkwood: 6
House al-Malik: 3
House Li Halan: 3
House Decados: 6
The Hazat: 4
This is a problematic distribution, however: we're told that the Advocates (those who voted for Alexius) numbered 23 of 35, but these numbers seem to stack up so that the Church, League, Hawkwood, Li Halan and al-Malik instead have 25. How to explain this?
One possibility is that the Church votes are split: instead of the Patriarch controlling all eight elector rods, he controls only three (the three the Justinian gave to him). The other rods are controlled by the various metropolitans, who during Vladimir's time seemed more neutral (as their metropolitae would have neccessarily covered the territories of several houses) than they do now, where their intrests align so directly with the five Royal Houses. If this is the case, the Church might have voted as follows:
Patriarch: 3 for Alexius
Metropolitan of Delphi: 1 for Alexius
Metropolitan of Criticorum: 1 for Alexius
Metropolitan of Kish: 1 for Alexius
Metropolitan of Cadavus: 1 against
Metropolitan of Aragon: 1 against
This then neatly leaves the Advocates 23 to 12 for Alexius, the two-thirds majority the Great Charter requires. While there are other possibilities, they are less neat and beg more questions - for instance, the Hazat could have stolen an elector rod from the Hawkwood during their raid on Leminkainen, or the League could have hedged their bets by voting 3 and 2 instead of all in favor of Alexius. More recent explanations for the division seem like they would have been mentioned, however.