Burrs for Guatemala

I bought a Mahlkönig Guatemala on German eBay about a year ago and I use it to grind for my plunger pot (FP). A while back I changed the habit of a lifetime and went over to drinking it black from the plunger, which was a great move: how much subtlety you mask by putting milk in it! The downside was that I became aware of quite a lot of fines in the brew. The grinder had been in use for many years in a bakery so I suspect the burrs are well worn.

The obvious thing to do is to get new burrs, but any I've seen online are very expensive: you'd get a good grinder for that! Head says I should just buy a new grinder for the plunger, but I like the Guatemala! It's retro style, it's massiveness, the power of the motor, the fact that it's still in production after decades...

So what should I do? Please suggest a new grinder or, even better, a source of cheap burrs!