Hi, Peter
Where to begin... the documents that are stated to be Materialverluste are the same documents that we all know as the Generalquartiermeister reports.
As Nick correctly states, for the first period of the war these documents carried the title "Flugzeugunfälle und Verluste bei den Verbänden am 10.4.1940" for the document filed on April 12th 1940.
Later on the RLM and Generalquartiermeister saw that there was no sense in using these titles, as even if the regime was to file the loss reports the same day, this was often not the case in practice, and the subsequent reports were filled with so-called "Nachträge" - addendums. The name of the document was then changed to "Flugzeugunfälle und Verluste bei den Verbänden" only.
I do not know what you are looking for specifically, but the RL signatures for the above mentioned documents are mentioned on my site which still exist on
www.stormbirds.com/eagles
I would however advise you, given that you are looking for information in the timespan 21.6.1941 to 31.1.1945 to contact me, as I have a better finding tool for losses from this period
Regards,
Andreas B