@neongod I got hold of a nextduino (which I think is pretty much a packaged tzxduino) fairly recently from here (www.youmakerobots.com/sinclair/77-nextduino.html) although I guess it depends where you are in the world.

Before that I cobbled together a solution using a cheap small mono amplifier boards I bought online, powered it from a 5v usb connection and put a couple of audio jack sockets on it. From that I was loading and saving using a digital dictaphone. I guess you could hook it up to any modern audio out though to boost the signal enough. (<-- completely untried)