Just a brief note to update this thread.
A search across a large geographical area, involving the assistance of friends & family together with planes, trains, and automobiles resulted in the delivery of a sack of grower pellets to my gate on Wednesday evening.
Pellets that the birds studiously ignored for the following three days.
In the meantime they've been having a ball eating up weeds and whatever creepy crawlies they can find.
Managed to coax the little dinosaurs into trying some pellets yesterday by giving them a very small amount of wild bird seed mix (devoured instantly), then adding a little more to the pellets. That worked, once they tried a few pellets they were happy to eat them.
Next hurdle is to convince them that the nesting box & house I spent days building, would be a good place to sleep at night...