"I did ask at the outset of this thread 'Does anyone know just how many are flying' and where they are?"
HZ,
That would appear to be a difficult question to answer as several US aircraft are technically on the register (Mainly ex-AAL bizjet conversions) but in reality no longer flying. There's a Yahoo BAC 1-11 group you can join & I beleive they have an annual list with a speculative number but...
The active operators I'm aware of are Northrop-Grumman (flying test beds),
Boscombe Down (QnetiQ/EPTS), TAROM or its successors, Royal Omani AF (slated for replacement next year with A320s) and that's about it - maybe a dozen. Don't know what happened to the one & only Dee Howard Tay-engined prototype.