Reflection Illumination 50/50 Splitter Sourcing

I have troubles finding any matching beam splitter / dichroic filter. Also the required dimensions are not mentioned anywhere in the the documentation. From what I measured 12.520.01.5 may be what I need? However, I mostly find filters/splitters at a thickness of 1.1mm and not 1.5. And nothing matching length/width at all.

Would it be practical to cut a larger filter to size?

I searched on Aliexpress, Ebay and some smaller European suppliers.