Another option would be to source a complete set of electronics from a donor car. Preferably with 2 fobs

they are listed on EBay from time to time.
You will need
ECU
BCM
TCU
SKREEM
ignition cylinder
drivers door lock
glove box if available

I believe the coupe and Roadster are different so you’ll need to ask the questions

I would strongly suggest that you ask for the title when purchasing. This should not pose a problem for the seller. If you’re selling off these items, it’s more than likely that the donor is already beyond repairable. Title will be required if you want to purchase a new fob in the future.

Prior to purchase, pull a vehicle report to discover the reason the donor car was scrapped. If it’s because of water (flood) take a pass.