Key fobs are available from various sellers/vendors. Here is one I found (I don't know this company so check before you buy).
https://www.ikeyless.com/vehicles/Infin ... 1/1000285/
To reprogram (enter new ID) Key Fob(s) for 1997-2001 Q45 and I30, maximum of 4 Key Fobs
1. Close and lock all doors.
2. Insert and remove (all the way) the key from the Ignition Switch more than six times within 10 seconds. The hazard warning lamp will then flash.
3. Insert key and turn Ignition Switch to "ACC" position. The new ID code is entered and original (previous) ID codes are erased.
4. Push any button on the new remote controller once. The hazard warning lamp will then flash. If there is only one remote controller skip Step 5.
5. Up to 4 Key Fobs can be programmed. For additional Key Fob (ID code entry), release the door lock, then lock again with the main door Lock/Unlock switch.
6. Remove key from Ignition Switch
7. Unlock driver side door, open driver side door and then close the door. (END)