You cannot buy OEM licenses. Those are meant for computer manufacturers like HP, DELL, Lenovo, Acer etc. Those are not sold to the public.
If you are talking about the disks that are bundled with laptops/PC s sold by manufacturers, then you will have to talk to the manufacturer customer care. I dont have any idea.
As far as I know, the disks that are bundled with the PC/Laptops dont have serial numbers separately. Those are the auto configured install disks. Just pop in the disc, sit back and relax.
The discs that came with HP PC's bought by 2 of my friends around 2 years back were like this. One had XP and the other had Vista.