How do I obtain a chipdata file for the 12f1840 device?
Until there is an official release of a dat file for 12F1840 the quickest solution would be to copy and edit the dat file for the 12F1822 - there aren't many differences between the two so there's not much editing required.
Open the 12F1822.dat file in a text editor and save it as 12F1840.dat then make the following changes -
In edit 2 of the lines to look like these
In edit the section to look like this
I can't see any other differences - the peripherals look the same and the configuration words are the same.