We have found finally a producer that has access to pogo pins at the same picth as the one in the HP calculators. It is a different pitch from the industry standard 2.54mm - which makes it difficult to find a replacement.
Now we are discussing the prices - prior to this, we did not even know with whom to discuss! Let's hope to strik an agreement and be able to have a product for Christmas.
Here are some pictures now drawn by the factory: