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.
I don't have specific sources for shell tonnage, but yes, German artillery was still a big deal in 1945.
In fact, during all the war, German arillery was something to deal with: Usual German units had a sense for placing them, since they were part of their military culture. They had sometimes observation aircraft, and motorized units had trucks for their artillery pieces.
Speaking of 1945, there were different types of artillery usecases:
- Defending a line: The Siegfried line was occupied at last by several units out of scratch. They had mortars, guns and antitank guns as much as they could and it prevent them for being overran too fast.
- Converted anti aircraft artillery: Remember that Allied conducted heavy bombings of Germany during the war. Plenty of anti aircraft artillery was deployed to counter that. When Allied armies invade Germany, they encountered in the Ruhr big "Flak" zones in which antiaircraft guns were used against tanks and infantry. This conducted to heavy tank losses at the begininng, but using the cartography of the zone made by air forces, Allied land armies managed to overran and encircled them.
- Coastal and ship artillery: Commonwealth soldiers faced near Hamburg ships in harbours and coastal artillery turning their guns against them. This was quite efficient since they had longer ranges.
So yes, artillery was a thing at that time.
Now, if you want to support the claim of German artillery involved in a battle, use the battle of Seelow: During this battle, German forces used 2 600 artillery pieces from the hills to pin down Soviet corps for several days. Bad Soviet preparation did not allow the more massive Soviet artillery to counter it for the first days, and Soviet tank and infantry losses were high.