Promag is manufacturing 10 and 15 round magazines for the sub-compact Kel-Tec P3AT & Ruger LCP
The 10 rounders cost about $32 and the 20 rounders are going for $35, although you may be able to find them cheaper at other sources.
And now, before you ask “why?”, I say “Why Not? :)”.
[ Many thanks to the reader who sent this in ]