As we can guess, the original GN drives were built a in time period after Scheolias death, and revival of CB, and only 7 were built(i think I translated correctly, but i am not sure, it was from a bad scan through one of the strange looking gundam forums)
Ands so we can see that 5 of them are already in use...
however on other side I found this ->> "The GN Drive, also known as a solar furnace, is the power source of a Gundam. It harnesses photon and positron discharges of the non-evaporative decay of baryonic matter as an energy source. Its use is unlimited but it has to undergo recharging once in a while.
GN Drives seem to be able to be created anywhere. But it is suggested they were first developed at Jupiter after finding data on the GN Drives on the Jupiter explorer. There are five original drives that were created a hundred years ago Only their filter, the TD Blanket, can be created there.
Celestial Being guards these drives with great secrecy and would destroy them than allow them to fall into enemy hands.
Unknown to everyone but Aeolia Schenberg, the drives have a hidden secret. If their full capacities are unleashed, then the mobile suit could go three times its normal speed. This function is known as Trans AM."