Do you know how hard it is to get resistors over
100 Meg. Lucky for us in the USA there is Victoreen
(They also make real good Geiger counters if the mushroom clouds come)
It seems Ohmite bought their resistor product line.
These thick film resistor datasheet is here:
http://www.ohmite.com/cgi-bin/showpage.cgi?product=v_maximox
In the USA since DigiKey should stock them they are our best bet.
Why do you need 3G?
This resistor only effects the low freq. pole of the mic?
Why do you need 3G?
The higher you go above what you really need is inviting trouble.
From surface leakage. And grid currents in tubes.
These guys also do thick film HV resistors.
http://www.ebgusa.com/
One of the famous mic guys use this resistor company SRT
http://www.srt-restech.de/
Datasheet
http://www.srt-restech.de/engl/downloads_e/gsteng_neu.pdf
These guys do very good thick films.
http://www.ohmcraft.com/ohmcraft/datasheets/HVR/ds-hvr2.php
But most of these product will not be in stock as they are build to order!
I do not hink many here have had to source these speciality parts for a living. Go ahead and get some quotes from these guys. I doubt you will
find off the shelf vendors.