I don't have the time and/or patience to do the math, but I believe that there are at least 2 shabbatot rosh chodesh per year that aren't otherwise holidays where we would lein the Rosh Chodesh haftorah. Machar Chodesh is a little less likely only because if Rosh Chodesh is 2 days, and one is shabbos, we lein Shabbos Rosh Chodesh and not machar chodesh.
Regarding ר"ח lots of times we do not lain השמים כסאי
חנוכה, שקלים, החודש, ראש השנה, (וי"א ג' דפרענותא וז' דנחמתא )
So it may happen that we lain it twice in a year but definitely not every year