I can add to this as I recently received an offer for a Black Box leather Kelly (BBK). It's my absolute holy grail and I am so excited I finally got the call from my SA.
I remember about 3 years ago after a few purchases I enquired about a BBK and the SA helping me at the time gave me a smug smile and said "That's just not possible you will be waiting for 5 years" I told him politely that I was willing to wait and went on a mini rant about my love for heritage leather and he still dismissed me. I took it as a sign and switched SA at the same store (I was just starting to build my profile - so it was not a big deal)
When I told my current SA he got so excited about the BBK but managed my expectations and in his own words explained the "push offer" without using that term. In the last year I got about 3 Kelly offers (epsom, chevre, togo) and a Birkin Grizzly - all declined because I was patiently waiting for box.
Now that it has arrived in store I simply cannot wait to pick it up

Long story short - find an SA who understand your love for Box and is willing to help you - let them know your wish and be prepared to be patient and strong to decline other offers if you wish so.
Best of luck!