You can use a For Each file In FileList() loop for that, there is even an example in the HELP that does pretty much what you want:
// list all QV related files on disk
SUB DoDir (Root)
FOR Each Ext in 'qvw', 'qva', 'qvo', 'qvs'
FOR Each File in filelist (Root&' \*.' &Ext)
'$(File)' as Name,
FileSize( '$(File)' ) as Size,
FileTime( '$(File)' ) as FileTime
FOR Each Dir in dirlist (Root&' \*' )
call DoDir (Dir)
CALL DoDir ('C:')
If you want to read xls files, use the appropriate extensions in the filelist (...in 'xls', 'xlsx') and create an appropriate LOAD statement in the loop body.