The double struck (blackboard bold) lower case gamma is part of Unicode, as well as the upper case gamma, lower and upper case pi, and upper case sigma (but actually that is the double struck sum symbol, that happens to be a sigma).
If you have a (math) font that defines these characters then you can use them with the unicode-math
package with XeLaTeX or LuaLaTeX. Various fonts have a different design for these characters, so you can choose which one you like best.
Code with some examples:
\documentclass{article}
\usepackage{fontspec}
\usepackage{unicode-math}
\begin{document}
\setmathfont{Symbola}
Symbola: $\mathbb{\Gamma\gamma\Pi\pi\sum}$
\setmathfont{DejaVu Sans}
DejaVu Sans: $\mathbb{\Gamma\gamma\Pi\pi\sum}$
\setmathfont{DejaVu Serif}
DejaVu Serif: $\mathbb{\Gamma\gamma\Pi\pi\sum}$
\setmathfont{Code2000-rdLO.ttf}
Code2000: $\mathbb{\Gamma\gamma\Pi\pi\sum}$
\setmathfont{STIX}
STIX: $\mathbb{\Gamma\gamma\Pi\pi\sum}$
\setmathfont{seguisym.ttf}
Segoe UI Symbol: $\mathbb{\Gamma\gamma\Pi\pi\sum}$
\setmathfont{Asana Math}
Asana Math: $\mathbb{\Gamma\gamma\Pi\pi\sum}$
\setmathfont{Latin Modern Math}
Latin Modern: $\mathbb{\Gamma\gamma\Pi\pi\sum}$
\setmathfont{STIX}[range={\Bbbgamma}]
Latin Modern + STIX: $\mathbb{\Gamma\gamma\Pi\pi\sum}$
\end{document}

This example is largely based on https://www.fileformat.info/info/unicode/char/213d/fontsupport.htm (click 'View All' to see the gamma character in the fonts that I did not include in the code above).
Note that \setmathfont
changes the font for all math characters, however you can also set the font for just a single character using the range
parameter, as shown in the last example. The codes for the range can be found in the file unicode-math-table.tex
.
unicode-math
. See fileformat.info/info/unicode/char/213d/fontsupport.htm for a list (click on View All to see the actual character rendering). There are many different approaches in the design of this character, maybe you find one that you like.