Most non-specialist stores, including office supplies chains.
Some of the discounted PCs, typically configured with Windows Home Edition, won't even work properly with Linux. I destroyed an Asus notebook's motherboard by reformatting and installing Ubuntu Linux. The tech who diagnosed it suggested that the Linux drivers may have set some I/O registers in a way that caused the fault.
"Bargain PCs" tend to be manufactured to a very low cost, so they have many compromises in order to meet those targets.