thank's a lot @6x7II for your DIY!
With my K-3, I used a screen from focusingscreen.com (K3) and searched for one for the K-1 and found your post.
I ordered a Canon Ec-A (like the microprism more) and cut away the nose. The part which needs more time was adjusting the new
shim that it's correct for focusing - with the original shim (~0,58mm thick), there was a huge front-focus.
So I decided to make a CAD-drawing of the original K-1 shim and then printed some of those with my 3d-printer.
The print quality is not that nice because the shim width is very thin but it holds in place and I found the thickness I need (~0,32mm).
I'm very happing because it's working great and right now the focusing with Samyang 135mm F2 is a lot of easier!
If someone want the cad drawing - feel free to ask...maybe someone has got the possibility for lasercutting or something else