You want to buy them new or used? You can only get them at a dealership. Most xj's come with one strip on the passenger side and you have to buy the driver's side nut strip from the dealer. I did this and there's a thread here on it.
Part numbers 52001174 (right) and 52001175 (left). I think they are $27 each. Worth it though.
2001 Sport 4.0 30/8.25 Flux Capacitor Heat Machine
Black XJ club member #1