I think the CO and DO car situation is a bit of a mystery to say the least, and may merit some further investigation since it seems to vary on a country-by-country basis.
I know that in the UK cars are bought by the Society for travelling overseers, but they have to return them to the society after a period, whereupon the Society sells them on (at a loss) to the BROTHERS! The last I knew the COs and DOs were being issued with brand new Vauxhall Astras for everyone across the board. Prior to Astras, they were issued with Vauxhall Vectras (which is now the Insignia). Every four years or so the COs and DOs would have to turn in their cars to bethel who would then flog them to brothers via announcements made at congregation meetings throughout the UK!! I always thought this was a very distasteful practice, reminiscent of the traders in the temple, and I felt that way even though I was a die-hard witness at the time. I don't know whether it has changed in the last couple of years, but I can't imagine it will have done (I would welcome any needed correction from UK witnesses on this).
However, I know that this method isn't used in poorer countries such as the Eastern European country in which I currently live. By the sounds of things, in the US cars are LEASED for travelling overseers, and BOUGHT in England - whereas I know for a fact that in poorer countries, COs and DOs get no car from the Society at all! Yes that's right, they need to fork out for a car out of their own pockets, or hope that some of the brothers they visit will feel sorry enough for them to donate a car, which often happens. Whatever car they end up with, you can be sure it isn't a top of the line brand-spanking new model like it would be in the US or UK, but an old banger that nobody else wants.
The injustice of this situation was driven home to me when my wife and I had lunch with a CO and his wife while we were in the UK. The CO had just had to return his Vauxhall Vectra and had received a brand new Astra as his new car. He was actually COMPLAINING because his new Astra wasn't as big or as comfortable as his beloved Vectra that he had just been forced to return. Mrs Cedars and I were quietly disgusted because (1) at the time we were driving around in an old 1997 Rover 25 which had all sorts of problems with it, because we were pioneering and had little money with which to fork out for anything better, and (2) because Mrs Cedars came from a country in which COs weren't given cars at all, but had to make do with any old rust bucket they could get their hands on - and here we were listening to a CO complaining about his brand new Astra that he didn't need to pay anything for!
Seriously Marvin - it would be VERY interesting to do a country-by-country analysis of the travelling overseer car arrangements, as I think everybody would be surprised by how much such a simple thing varies in our "united" global brotherhood.... Why don't you ask everyone to PM you with how things are done in their respective countries? The results might be eye-opening.
FYI - here is what a Vauxhall Astra looks like...