Apologize for the delay in sending this.

I created a simple project of UXGridView (bind to WCF RIA services using MVVM pattern) and implement data filtering using UXDataFilter control.

How do I simply use the itemsource for UXGridView as my source for filtering?

I assume that you want to bind an identical data source to UXDataFilter and your UXGridView. UXDataFilter supports both client and server data operation. When you set the QueryOperation to Client, UXDataFilter will process the data paging operation in the client against the given data source.
For more detail, please run the attached sample project, and open "Customers" page.

Hope this help.

No, I simply want the built in filtering of uxgridview to provide filter options based on the itemssource of the uxgridview.  So if there are 100 items in my grid and I am filtering by category which only has 10 possible options.  I don't want all 100 items to show up in my filter box. I simply want the 10.  It seems that this should be built in somehow but I feel I am missing something.

For column filtering to work properly, we need to specify FilterItemsBinding, FilterMemberPath, and FilterValuePath properties to each column that supports data filtering.

You can try to select distinct of category to have the 10 items to show up.

Example:

var countries = enumCustomers.OfType<Customer>().Select(p => p.Country).Distinct();