Here is a BAT file that should do the job for you:

setlocal ENABLEDELAYEDEXPANSION
Set SOURCELIST=X
for /f %%f in ('dir /b \\testserver\dir\*') do set SOURCELIST=%%f+!SOU
+RCELIST!
set SOURCELIST=%SOURCELIST:~0,-2%

echo ==%SOURCELIST%==

copy %SOURCELIST% dest\testrpt.txt
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