Ah ,I see the model, referred to as a 'GIBB foot block' on the Rig Rite site,and can see why you want to match the pattern.They look very strong and durable and would nest neatly.I can see from the Seal manual that ,yes,they were original - they appear on the Detail Rigging sketch page.
That being the case,and if the model reference makes sense, maybe someone in the States will buy and forward to you.There is at leat one member there with a 26/27.
My son lives in Manila and with the same problem uses an intermediary agency in California to buy stuff and ship to him,but they only deal with the Phillipines.
Do Rig Rite not have any suppliers in the States who would do this ? Surely they supply other chandlers/shipwrights.
One could be made ,although the finish would not match.But ,assuming its neighbours are still black,you might ,for a lower load,do something with black delrin/acetal,which would be easy to work and provide a convenient thickness.
As you say you could operate from the mast ,being s/h I prefer to operate the pole uphaul from there,whilst forward.
But I sense that you want the rig to be entirely ship-shape.
Peter L
PS If you can provide a close up photo or use the specific Rig Rite reference in a post on the Practical Boat Owner forum (much more traffic) someone might put their hands on one.