Two criteria (via dropdown lists) to get single result

I suspect this should be a pretty simple solution. I've set up my 2 dropdown lists, but need to use a formula (through DATA>Data Validation>Source) so they will acknowledge each other and provide a relevant list

Something to the effect of BRAND:MODEL (brands have multiple models and model numbers can apply to multiple brands)
By selecting a specific Brand, the Model Dropdown List will show all relevant models. And vice versa.

I've only gotten to the point that the dropdown lists will only display the first result.

I used (and modified) the following formula:
=IF(C2="",RegionList,INDEX(RegionColumn,MATCH(C2,CustColumn,0)))

where C2 is the Customer and B2 is the Region

How do I get the dropdown list choices to update each other to MULTIPLE results?

Thanks in advance.

Check the below links to know how to do it

http://www.contextures.com/xlDataVal02.html

http://blog.contextures.com/archives...ists-in-excel/