I have owned some matching examples in my years of collecting, and at one time they were not that difficult to find. Not easy but not the hardest things to find. As the interest in WW2 seemed to increase, matching German k98 rifles in original configuration have definitely dried up.
I can remember how I used to travel hundreds of kilometers to meet up with a seller of an "all matching" rifle, only to find that it was a badly sporterized job, peened piece, or an M48. These were the days before the internet. I miss those days sometimes though.
But those were the days before I was married, and my passion was strictly the K98 rifle. Now my passion is my kids, family first. So I sold many of my rifles, including a few matching examples.
In recent memory, I have paid as little as $300 for a correct piece, and the last one I bought cost me close to $2k. I personally believe these are overpriced for what they are, still when you are driven by such a strong desire as milsurp collecting the k98, what is a guy to do? All reason goes out the window

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I really believe the capture pieces are outstanding, including the Russian ones. So full of history, and quite affordable, for now. We should all have Rcs in our collection.
How many matching are out there? I have no idea. I do know I am not the only guy on this forum who owns righteous matching examples. I also know there are a few that are represented as matching and original configuration, but truly are not, so heads up if you are buying.
The Germans, during WW2, never issued their rifles with a bayonet that was serialed the same as the rifle. The only exceptions to this that I know of are the contract pieces Mauser produced, for the Portuguese as an example (please correct me if I am mistaken, Gentlemen). It is getting increasingly difficult to find bayonets that are serialed the same as the scabbard though.
Here are the all matching and original configuration pieces I still own. I kept these as they represent early, mid and late war features generally speaking. They are a DUV41, BCD/AR42 and a DOU44. Thanks for looking, sorry to be so long-winded, but like I said, it's a passion.