Allegedly the German logistical system had broken down by 1945. Yet they still fought many tough battles. I would like to test these claims by looking at monthly shell tonnages in 1945. I believe that they were consuming around 2 million tons monthly most of the war.
You can see some statistics on gun production here. Production held up to the end of the war. Note that the major industrial areas in Germany were never lost. The Allied bombing killed many people but there was really no way it could affect dispersed large scale production of artillery pieces and shells.
I am sure that the shell tonnage statistics exist somewhere, however I can't seem to find them. However the Germans continued to make major offensives to the end of the war, like Balaton, which although unsuccessful inflicted massive casualties.
A source for you may be Waffen und Geheimwaffen des Deutschen Heeres 1933-1945 (Weapons and Secret Weapons of the German Army 1933-1945) by Fritz Hahn. I don't have a copy myself, but this page of German Weapon and Ammunition Production claims to use it as a source.
As you can see, production fell off precipitously for most weapons in 1945, even accounting for the war only lasting 5 months. Though chaos of German record keeping in 1945 might account for that. Hopefully the book itself will provide more detail.