As far as I know Mittelbau-Dora was a subcamp of Buchenwald not of Auschwitz. There is a website about Buchenwald and Mittelbau-Dora.
At the end of the war many prisoners from Auschwitz were sent to other camps like Mauthausen, some with trains, but many on the so-called "death march".
The Arolsen Archives have some records of Mauthausen online, but there is also a website about Mauthausen camp.
The deceased of the Mauthausen Concentration Camp
Did you seearch with different spellings of the surname on the Arolsen Archives? Sometimes I found one and the same person with different spellings there.