The remains of the Lockerbie 747 are at a scrap yard in woodhall spa, lincolnshire. The engines from the BA 777 are down at Kemble.
The reason the 777 engines are at Kemble is simply because that's where the aircraft was sent for scrapping. If ASI could find a buyer for two slightly bent Trents, I'm sure they would sell them.
AFAIK the Lockerbie 747, on the other hand, can't be scrapped as it's technically still evidence in an open crime investigation.