Blackboard bold variants for Greek letters

The mbboard package provides blackboard bold Greek letters, and the letter you want is \bbmu. However, I don't know if you like how the symbol looks. (I don't like it, actually.)

The mathbbol package with the bbgreekl option also provides (a possibly nicer version of) \bbmu: Use \usepackage[bbgreekl]{mathbbol} in the preamble. The disadvantage is that the package also redefines \mathbb; see this post for possiblities to avoid this.

Note that lowercase epsilon is typeset with \bbespilon (sic).

Edit: I just realised that the mbboard package redefines \mathbb, too. If you don't like this, then an easy solution is to load the amssymb package after the mbboard package. This gives you the "usual" blackboard bold letters, and you can still use \bbmu and friends.

Another font set that can provide this is MathTime Professional II fonts (mtpro2) from PCTeX. The web site mentions some journals that use these fonts.

The fonts are non-free and, to achieve what is wanted here are, chargeable (the non-free but no-cost 'lite' version does not include the 'blackboard bold italic' and 'holey bold italic' fonts which the two samples below use, using a simple redefinition of \mathbb). The outputs are just .pngs of screenprints so don't use these to judge the resolution of the original fonts.

\documentclass[12pt]{article}
\usepackage[mtpbbi]{mtpro2}
\begin{document}
$\mathbb{\mu} , \mathbb{M}$     % assuming '\Mu' = 'M'
\end{document}

\documentclass[12pt]{article}
\usepackage[mtpbbi]{mtpro2}
\begin{document}
$\mathbb{\mu} , \mathbb{M}$
\end{document}

I also spent a lot of time on the issue and found nothing satisfactory. So I made up my own blackboard bold mu and alpha:

\documentclass{minimal}
\usepackage{amssymb}
\newcommand{\Balpha}{\mbox{$\hspace{0.12em}\shortmid\hspace{-0.62em}\alpha$}}
\usepackage{xcolor}
\usepackage{graphicx}
\newcommand{\Bmu}{\mbox{$\raisebox{-0.59ex}
  {$l$}\hspace{-0.18em}\mu\hspace{-0.88em}\raisebox{-0.98ex}{\scalebox{2}
  {$\color{white}.$}}\hspace{-0.416em}\raisebox{+0.88ex}
  {$\color{white}.$}\hspace{0.46em}$}{}}
\begin{document}
$\Balpha\quad\Bmu$
\end{document}

This produces

_{(source: uni-muenster.de)}