Which engines could be used ?
The EJ200 of the Eurofighter produces 64% of the thrust of the Olympus, so that may be a choice for a 1:2 replica. Maybe somebody would even be happy to sell some, as probably that aircraft will not be produced in the numbers once forecasted, nor will it be in service for 50 years (like some other western fighters).
However, I seriously doubt that a 1:2 replica would cost only 50% of a real Concorde. You still need 99% of the know-how. So it probably still is simpler to bring a real one back to the air.
The one in IAD is most probably the one in the "most airworthy" condition anyway.
There's still an AF Concorde on a bridge at Toulouse - you can see it over the other side of the airport from the main pax terminal.
Not been around it myself, but I'm told that from an engineering perspective it's being used for ground engineering training so probably quite good, but from a cosmetic perspective it's pretty horrible.
That poor "cosmetic perspective" goes down to the bone... That airframe sits outside for over 10 years now, and even if the Toulouse weather may be slightly more favourable than the Filton one, it still takes its toll. Seen it about 3 years ago, and it probably does not look better today.