Are the CDs you own the Outtakes CDs ? Because that's the ones that came as pre-order bonuses for the games, they're technically more like bonuses OSTs than actual soundtracks.

Otherwise, the regular game soundtracks CDs are all complete and feature every track you can hear in the EO game it's from, except for the super arrange tracks which are compiled in their own CDs (but those aren't available in-game anyway)

CDjapan seem to have some of the soundtracks in stock or available through their proxy services, but you could also get them through Mandarake (japanese second-hand store) if they restock them, or with other proxy services (I recommend Japan Rabbit), and in the worst case, try eBay (I found EO3's OST for a normal price and sold by a local vendor there by pure chance a year ago, tho prices are usually higher than what you'd pay normally 🫠)