You didn’t say what kind of wood your Mollenhauer Denner alto is made from. I have read that palisander (rosewood) can cause allergic reactions in some people. I suggest that you make an appointment with an allergist (if you haven’t already done so) and get checked out for various wood allergies (not just dust) before you invest in another wood instrument. If the allergic reaction turns out to be indeed triggered by the cedar block rather than by the wood of the recorder itself, you might ask a reputable repair shop whether they can make a new block out of some wood that you are not allergic to (hoping that there is one).
Since very few people on the various forums post follow-up replies, I would like to ask you to keep us informed of your discoveries and decisions. While I am not plagued by allergies such as this, I am sure that there may be a few out there who would benefit from learning what you might learn.