The immo on those is easy.And relatively cheap to fix as well.Easiest to buy a 2nd hand immo box with the same p/n that comes with the pin.Then all you need is vcds, box with unknown pin is tricky but doable if it comes with a transponder that is matched to it.I'd expect fixing would cost <£100, an immo delete won't cost significantly less.
I will be on the hunt for another Mk3 once lockdown is over, and I am hoping that this https://carplus.co.uk/car-finance/no-deposit/ is the reason for the current lack of them advertised for sale.