the link goes throught to ihs but even ordering from the states it shouldn't be a long. Some standards can be downloaded but the security features can be a bit troublesome.
BSI global advertise B313.3, but have no price as yet.
There's ordering information right on the site. I believe the new edition is coming out this summer, so unless you need it urgently, you may wish to wait.
You might also want to pick up a copy of Dr. Charles Becht's book on using the B31.3 Code - it is an ASME publication. Also, Glynn Woods wrote a book on B31.3 that is published by CASTI Publishing.