There are many ways to get those file.
MSCDEX.EXE is part of DOS. If your DOS copy came from a complete installation, you should have it, under C:\DOS.
On most of my machines, I’ve been happily using VIDE-CDD.SYS driver. It has a very small memory footprint, and is very compatible. Although not 100% compatible, it works with most drives and most programs. You can get it, for example here:
https://vogonsdrivers.com/getfile.php?fileid=1456
