Hi Doug Matulis,
Greetings from Syncfusion Support.
We have reviewed your query and understood that you need
to set the custom dataSource to the dropdown edit of a column. In the
column.edit property using the params, we can provide the custom dataSource to
the dropdown. We have already documented this topic in our documentation. The
documentation link has been attached below for your reference.
Documentation: https://ej2.syncfusion.com/aspnetmvc/documentation/grid/editing/edit-types#provide-custom-data-source-and-enabling-filtering-to-dropdownlist
We have also attached the sample and video demonstration
implementing the customer dataSource to the dropdown edit of the column in the
MVC platform.
Image:

Please find the sample and video demonstration attached
below.
Regards,
Dineshnarasimman M
Attachment:
MVCGridSampleCustomData_3b7da08c.zip