Many online jewelry sites will let you order a ring using a measurement from a different country. Not every jewelry store online allows for only United States system of measurement. Here is some information on what other parts of the world use for ring measurements.
In Britain, the GB (Great Britain) ring size scale is used for measuring a ring finger. This is a scale that is alphabetic. Many online sites offer ring sizes from H to Z plus 4.5 for rings. Some offer half sizes also.
In Australia and New Zealand, a similar system to that of Britain is used. The AU (Australian) scale is used which is also an alphabetic scale. The sizes available are usually similar to what is available in British sizes.
In Asia typically your ring size will be a larger number when compared to United States sizing. For instance, if your ring size in the United States is a size four, your ring size in Asia will be a seven. Try doing an Internet search for more information on ring sizing for Asia.