If you create a new Custom Field in Gravyty but do not see it pulling over into Importacular for you to map, it is likely that a final step is needed to be applied in Gravyty.
It is not uncommon that the new Custom Field has not been associated with the appropriate campaign. As Gravyty is a third party application in Importacular, you may be better served looking to Gravyty's support pages for up-to-date information on how to do this.
However, in an effort to be helpful, please try heading to Gravyty and, in the appropriate Campaign, head to 'Advance'. Here, you should be able to add the new Custom Field to the Campaign. Once you have done that, head back to Importacular, re-run your Gravyty Data Source Criteria. The new Custom Field should now be present.