There's two slightly different holders that fit 9x12 Patent Eutui's.
Have a look at this thread on Photrio. You'll see I've posted Illustration of the numerous edge types.
Essentially the thickness of the lip was changed at some point = I have 2 and the holders that fitt my one (currently in Turkey) don't fit the other but are more standard and fit a few of my 9x12 cameras.
They are amazingly small LF cameras when you think 9x12 is almost the same as 5x4 just narrower on the long edge.
With a Graflex Crown Graphic and 6x45 Ikonta,520.
My main Patent Etue with a more Typical German 9x12 camera, I think my Rodenstock (Welta). Mine has a 135mm f4.5 Tessar.
You will also need film sheath inserts for 9x12 plate holders but these are standard. While I still have a lot of metal 9x12 plate holders I've none spare for Patent Etui cameras.
Finding holders is rather hit and miss, I bought 3 boxes with maybe 300+ metal plate holders of various sizes some years ago.
Had you needed 6.9x9 Patent Etui plate holders I could have helped as I have 3 cased sets of 3.
Ian