You certainly can, but not directly from giffgaff as unfortunately they currently only send SIMs to UK addresses. However many giffgaff community members are happy to help - look for community members' signature links or banners advertising that they are willing to send SIM cards abroad, then contact them directly.
You can also find details of a randomly selected member that has indicated they are willing to send SIM cards abroad by visiting this topic.
Please note that goodybags only work in the UK and giffgaff to giffgaff calls and texts are only free whilst you are in the UK. Using a giffgaff SIM outside of the UK will incur roaming charges. Details of the charges that will apply can be found here.