ASX300, page-35

So it's not purely based on MC. For example take MGW, VG1 and IAF ranked 249-251 by market cap on the ASX according to your market index site. None of these entities are in the ASX300. I don't know exactly why, but they aren't eligible for inclusion. As a side note Morningstar don't have a recommendation for them either and I'm sure it's for the same reasons.

Best you can do is look at the ASX300 list and sort by market cap (go to ASX300list.com). Then compare the bottom MCs with your company of interests MC and see where it would sit in that list. Remembering that inclusions aren't based solely on MC. So companies in the list with a struggling MC aren't automatically kicked out, and your company of interest is also competing with other emerging and growing companies that are vying for an inclusion too.

Even though according to that index we sit 443 of all listed companies, with a MC of $325m we'd sit 275th on the ASX300 if we were in it.