Anyone know how to add this field (corporate card) to a transaction saved search? Additionally, is there any documentation to map the field ID’s to the name in the saved search list? I’ve found them to be very inconsistent.

You might have some luck with the records browser. Search help for "SuiteScript Records Browser". For that particular field, if you cannot see it in the list, it may not be available in the list, you may need to use a formula for the column.