# [Python 3.8 (pre-release)], 90 bytes

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    lambda s,e,n:[d for i in range((e-s).days+1)if-len(set(d:=str(s+(e-s).__class__(i))))==~n]

An unnamed function which returns a list of strings (counting/including leading zeros) that accepts three arguments:

* `s`, the *start* - a `datetime.date` object;
* `e`, the *end* - a `datetime.date` object; and
* `n`, the number of days - an `int` object.

**[Try it online!][TIO-k1jb0lj9]**

Note: As the function accepts `datetime.date` objects I have not counted the import code for that (and have worked around importing the `datetime.timedelta` object as it is indirectly accessible via subtraction of these input objects). 

[Python 3.8 (pre-release)]: https://docs.python.org/3.8/
[TIO-k1jb0lj9]: https://tio.run/##VY3LCsIwEEX3fsUsJzQVa0XbQr5EJUSTaKB5kMmmG389Wl15dvdw4aSlPGPoh5SrzdGDVsUU5w04n2Iu372x4lJn5W9aAXHDw3TWYGMGBy5AVuFhEE1LbKvVQk3HnG1nE5BMQT0JKhmp@R2kvM@KSEp07IMQr3CtKbtQ0OLawu50GDkcOex3jMO/6lc1MFbf "Python 3.8 (pre-release) – Try It Online"