Last time this came up, I spoke with some retailers, who said they record all serial numbers on kites they sell, so if yours is stolen & you didn't record it, you can try asking the shop for the number.
Regards an online register here - it's a great idea, and it's in the "ideas hat" .. so many ideas, and only so many resources to build stuff, so it won't happen overnight, but it will happen...

Thanks for your patience.