Pete, have you dealt with Giant parts before? Only reason I ask - they tend not to stock proprietary parts for very long. I had a friend who had a Giant Halfway folder that he needed some parts for, and he was told by Giant they no longer stocked or sourced them. The LBS where I hang out is a Giant dealer and confirms that parts availability is somewhere between scarce and non-existent, especially on older-model low production bikes like folders and recumbents.
Your best bet is to contact Giant directly, or a Giant dealer, and see if they can help you, if you need something like their proprietary chainguard. If it's not a wonky BCD, you might be able to replace just the chainring, but it is not an elegant fix.