The three records are somewhat different. The Riverside was reissued (with most of Riverside's records) on Washington as WLP 711 "British Army Songs." There are a number of LP resale websites. You might get lucky.

On the other hand, quite a few have been reissued on CD. Maybe they just haven't gotten around to these yet. John Ross keeps as up to date as one can... see http://www.well.com/user/johnross/discographies/ewanmaccoll.htm