On Military Matters are the current publisher of Arty Conliffe’s Crossfire. The rules and the Hit the Dirt supplement are available in both the USA and the UK.
In the USA, you get them from On Military Matters. Just Search for Crossfire and you also get Hit the Dirt.
In the UK, you can get them from Caliver Books. They have both Crossfire and Hit the Dirt.
There is no PDF option as yet. To date Arty has resisted this approach to publishing. For the moment it is paper all the way.