On many keyboards, the <Alt> key acts as <Meta>, so try it.
Instead of typing M-a, you can type <ESC> a. In fact,
Emacs converts M-a internally into <ESC> a anyway
(depending on the value of
meta-prefix-char). Note that you
press <Meta> and <a> together, but with <ESC>, you press
<ESC>, release it, and then press <a>.