I tried to do that mercury on aluminium experiment several times, but could not get it to work due to the near-instant re-oxidation.  Only when scratching the oxide away after already covering the aluminium with mercury was there a very slight reaction.

Anyway, it could be that this order was cancelled simply due to the extreme fragility of the SLI/H sodium lamps.  Even during the peak of manufacture in the 1980s there were immense problems due to lamp breakages during postage, and they were normally only allowed to be transported vertically on full palettes.  As soon as they are moved around when horizontal, which is typical for a long thin package sent individually, the risk of breakage is high.  My own experience when occasionally sending them to other collectors was that only half survived the rigours of the postal service, so then I also stopped.  It's too sad to send such a rare lamp knowing that there is a 50% chance of it being destroyed.

As far as I know the air transport companies do not make any problem about transport of sodium.  Certainly for commercial shipments of palette loads of sodium lamps there is not an issue.  But since about 2012 there are limits on the allowed mercury content specifically for the reason of the video shared by Max.  Aircraft are typically made from aluminium, and if mercury-containing products become broken and it leaks out and the aluminium parts would be scratched, the results of the ensuing corrosion reactions might not be very desirable.