Renovation of Existing Property - Our Way to the House

I am worried about the carpenter. On 31.03. he was commissioned to build the frame for the kitchen sliding door. He said the wood (white oak) had to be imported from the USA and due to Corona he expects a delivery time of 4-6 weeks. After that, he could start, but he would get in touch as soon as the goods arrived. After four weeks (29.04.) I asked for the first time about the delivery status, he asked for another two weeks. So on 11.05. I called again: there was a major fire at the industrial port in Bremen, which also affected the imported wood warehouse. He is waiting for feedback from the supplier, who first has to sort out the goods still fit for sale and possibly re-import. He said he would contact me by Friday about how to proceed. There was no call on Friday and he was also unreachable. So I tried again on Monday: in five weeks he will come to install. Now the 5 weeks are over, but no frame installed. Yesterday I couldn't reach him (only voicemail, once an employee said "the boss will get back to you by noon") and today only voicemail again. But when my wife called from a different number, he answered immediately: He is still waiting for information from the wood supplier. He will contact again today.

Is it really so difficult to get wood for a door frame within 12 weeks? Under what conditions can I otherwise cancel the order and find another carpenter? Am I possibly obligated to accept the wood if it ever arrives (prepayment)? After all, it is an order of about €1,800 (material/labor not itemized in the offer).

There is his offer in writing and our acceptance of it. The rest of the communication was by phone.