@halirutan note it's `\[Gamma]`, not `[Gamma]`.
page = Import[
"http://reference.wolfram.com/mathematica/guide/ListingOfNamedCharacters.html", {"HTML",
"Plaintext"}]; namedCharacters =
StringCases[page,
"\\[" ~~ Shortest[__] ~~ "]"]; InputForm[namedCharacters]