Theres also one(still goes bang but in .50 cal) on gunbroker.com, and one more (barrel cut and welded) on gunsamerica.com
The same guy who has the one on gunbroker.com, also has an Inglis Boyes available here:
http://www.gunexchange.com/boys2.html
You guys are lucky in the US. It only takes money to get a Boyes. Here, we have to wait for a current owner to die before one becomes available.
If you are given a choice, find the earlier unmodified version with the round muzzle brake and the early bipod. The later flat style brake makes the rifle just a bit longer, so it doesn't fit into the carrier real well. Also the later bipod won't mount into the socket and clips under the auxillery battery box.
Now, let the debate begin: is it Boys or Boyes? I saw Boyes on the cover of an early manual. All the rifles I've seen just have R.B.mk1 and maybe the star.