The concept of international porting, per se, does not exist: numbers cannot be ported in and out of countries. However, depending upon how the current provider hosts and has set up the numbers there are often options available to lease numbers and to ‘re-point’ numbers them to our service, either via call forwarding (or via SIP URI - although is bespoke, please do contact us to discuss this method if you feel it may be required).
The first step is to contact the current provider of the number, discuss your requirement with them and seek their advice to achieve your aim.
Furthermore, please refer to Can I Spoof International Numbers? and Can I Purchase International Numbers?