Have they, now.
The Germans are expecting a massive haul of 105 new Leopard tanks. For a new forward brigade to be deployed on Russia's doorstep in Lithuania!

When, you ask? They expect to be ready by 2030. That's rocket-ship stuff.

I went to law school so I wouldn't have to do math, but that certainly seems to me like a lot less than 100 years. That's a lot of tanks - their entire inventory right now is only about 300 tanks. And building tanks is probably a bit more complicated than artillery or ordinance. So it seems to me that if Germany can increase their entire tank inventory by a third in about five years, they should be able to manage increasing their artillery supply in less than a century, if pressed.

BTW...how long do you believe it would take other countries to build that many tanks, from initial order to deployment? 'Cause while five years might be a bit on the long side....it might just be normal. How long do you think it takes the U.S. to build new tanks? From what I can gather, it takes the U.S. about two years to build an Abrams tank starting from an existing hull (they have plenty of old hulls that they just re-kit to modern equipment), and a capacity of about 300 per year. So if the U.S. placed an order for 300 new tanks with a hull starting from scratch, they probably wouldn't all be ready for deployment until 2029. Time frame for the newest model of tank, from initial order to first (not 300) unit being deployed, is currently projected 65 months. Actual time will likely be longer. So it would take us even longer than Germany to put 300 of those on the line.

In wartime, when you dismantle the civilian economy and turn every auto plant and bus manufacturer into an armored vehicle maker, you can vastly increase the speed and output. But in peacetime? Are you sure that your description of Germany's timeframe isn't actually a pretty good outcome?