This should simply your search, finding file names that ends with *.rdc
$currSourceFolder = "C:\MyReports\MDX\"
Get-Childitem -Path $currSourceFolder | ? {$_.name -like "*.rdc"}

or even a specific search with extensions only like

get-childitem -Path "C:/temp/" | ? {$_.extension -like ".rdc"}

both should give the desired result, obvuiously you can more parameters