Clippard parts are are available through a worldwide network of distbutors. I got my latest order supplied by a local stockist in the UK - cost just over £20 each
It's a pretty simple conversion once you have either bought or made a pump kit. Rail and body needs to be milled, wave spring fitted behind bolt and finally power tube spacer adjusted to seal o-ring. I've built two pumpmags from parts so far using XM15 kits.