Quoting you here so as not to go off topic in the SO thread.
Barenia is a push offer item so, no, can't be ordered at podium. If your SA knows you love Barenia, you can ensure you are on the list if a bag shows up. I will be honest though, I haven't seen a B40 in Barenia in-store in years. I'm not seeing anything right now but K25, B25, and an occasional K28. I would look at resale if you are ok with that.
Barenia bags in new silhouettes or designs that have not been done previously in Barenia can be ordered via Horizon but for a B40 sized bag you are likely looking at around $60K USD minimum which honestly IMO is insane. If you would be ok with that cost, it is worth bringing up a Horizon order.
And yes! Function is VERY important

It is easier to find HACs in Barenia than Birkins, but the HAC40 (I have it in Barenia/wool felt) is really best as a travel bag.