If you can't find a RIB shop, try looking for a rafting supply company in Oz or NZ. They should be able to help.
You'll need careful measurements, as there are about 4 different flavors of Halkey-Roberts valves: old and new, and both of those in long and short. There are also several knock-offs that look and operate like HR, but aren't.
As to the question above, the answer is maybe. Depends on the particular valve, and how much pressure you can put on it. You can get by with a plastic or rubber tube that fits against the outside of the bore of the valve body and a cross-piece of wire situated to depress the valve release (my buddy uses a scuba hose strain relief sleeve and a scuba tank.) If it doesn't seal well, though, you're going to need a good deal of air to keep up with the loss (meaning a foot pump likely won't work.)