From where I live (Philippines) , there seems to be no stock for 26.8mm seat posts. All other sizes are available except for 26.8mm; they don't even sell shims for that size. Currently I am forced to use a 25.4mm seat post on my bike.
Is it possible to use a 25.4 - 27.2 mm shim for that purpose? I've used beer cans and inner tubes for shims, but both options has led to the seat tube crimping as I tighten it down.