The PDF drawings for their low mount disc drawings should be good enough to get the relevant dimensions relative to the dropout right, even if the part itself isn't the right shape. Of course the ISO disc mount specifications from the Shimano frame builder materials are available if you don't want to copy from Paragon.

Shimano gives these dimensions as 78.1mm from axle to the forward ISO mount hole, 51mm from between ISO mount holes, and 39.9mm from the rear ISO mount hole to the axle. Axle slot is 10mm, ISO holes are 6mm, holes/slot should be slightly oversized and if it wasn't stainless, it would not be too difficult to make with a drill press and hand tools. The dropout needs to be shaped to clear the disc brake, especially between the ISO disc mount holes to make room for the pot.

ISO disc drop outs should essentially be a single flat plate though, so I have no idea what's going on in the example pictures. Care should be taken not to orient the disc brake such that the axle wants to pull out of the opening of the dropout when braking.