Fortigate is a proprietary vendor that tries to create vendor locks.
The Fortigate Tokens are known to be Feitian C200 tokens.
But the seed files, that are shipped by Fortigate can only be imported on Fortigates devices. They are probably encrypted with a secret company key.
You need to buy new hardware tokens!
Just in case - you could buy hardware tokens at NetKnights - https://netknights.it/produkte/oath-hotptotp/
There will work a 100% 