Hi peoples!
I have the same issue as you msflsim. Last week I was in contact with Andrew Goldberg on Neumann regarding this matter and here is three truths he told me that I thought I´d share with u guys:
1: They are all out of spare drivers(i.e bass driver, mid driver and treble). But they still have spare-parts for the electronics.
2: The bass driver from kh 310 will not fit in the housing of the o300
3: Andrew told me that there wasnt a good idea too recone the speaker.. (but I beg to differ, everything can be fixed/rebuilt)
3: The kh 310 is a better speaker in many ways. (my ass it is...

)
Right now I have my o300 on the table of the swedish speaker mastermind Janne, who is the official Genelec repair dude in Sweden. He told me that a lot of the speakers from around that era are using the same drivers, cones and spiders.. on friday (17/1) I will have an answer if it is possible to find identical replacement drivers, cones and spiders, from other places than Neumann for the o300.
/Rasmus