what We do here , for touring cyclists having parts needs that are not in stock , its a small town,
is for something that is not totally stopping the rider..
is Call Head 2 days ride down the road to the next shop down the coast they run the overnight shipped special order.
and it will be in their shop when the rider arrives.. [this is what happens for people on Campag equipped bikes]
Perhaps you learned how Poste Restante, USPS General Delivery works?
Have it sent to Yourself, to a Post office ahead of you on your route.
Estimate where, by the shipping time versus your daily miles covered.
./.