So, while it is hard to find some LHD (left hand drive) vehicles in Japan, it's not impossible. There are LHD cars in Japan, but these are usually private or grey imports, often done because the model itself is not sold in Japan, or because it's cheaper than buying from the local dealer, as is often the case with Land Rover. Meaning it's not a plot hole. You see it quite often with certain specific models. It's a pain to do, sure, but there's various reasons people will do it in Japan.
Also, I forgot to add, but it's quite common to see LHD vehicles around military bases that host Foreign soldiers. So, say soldiers from the US. They're often able to ship their personal vehicles over seas to drive on base and in the towns or cities they're stationed in. Since the US is LHD, well, it's only fitting those vehicles also reflect that. It's also quite common, after a long deployment, for those same soldiers to sell their vehicles to either a dealer, or local, as even though the vehicle is 'used' its LHD nature will earn it a premium price. The game has never specifically said there's a military base nearby, but that would give Sel a simple easy answer to the vehicle. Just claim that she bought the vehicle off a soldier leaving the country.