If you're interested in seeing more about what people are currently doing with ARM, check out the slides at http://www.goingarm.com/#2017schedule

For buying a machine, it depends on what you want. Desktops are coming out now, for example: https://softiron.com/products/overdrive-1000/

Server/HPC, there are quite a few coming online. The Cavium presenter @goingarm listed (https://www.packet.net) on their slides, might be decent for getting a cloud instance to try out. There are many others. A good place to start finding them is: http://arm-hpc.gitlab.io.

A nice thing about ARM is that you get lots of different micro-arch under a single ISA. Once the ball gets rolling there will be many processor choices to choose from, which I think is a great thing (however, in full disclosure I'm one of the authors, and I work for ARM Research for our HPC program..although all statements above are my own opinion and not those of ARM).