http://www.wargamingonline.com/catalog/advanced_search_result.php?keywords=starship+troopers has all the sourcebooks for sale as PDFs. Bear in mind that the MI army book has rules and stats for Power Armour, Exosuit and Marauder Platoons, Light Armour MI are in the Klendathu invasion book, and Pathfinders get their own book, so collecting the stats for allof them can be a bit pricey.
And while the 1e rules are more complex than evo, they're not Squad leader or anything. it's the same core rules, just some changes, and ost of them aren't that bad.
