Echidna Wars DX is available for purchase at DLSite: https://www.dlsite.com/maniax/work/=/product_id/RJ187640.html (¥1540, roughly $9.67 at time of commenting)
I would recommend supporting the original creators, who are cool and deserve support for making a very cool game
Echidna Wars Mini, the original, is still technically available at D-Gate's site https://d-gate.sakura.ne.jp/mini_wars/game.html however, in order to access it through that URL, you'll have to jump through several hoops, including using an old version of java with worse security features and an old browser program that'll accept the very out-of-date java version.