The chip you will buy from the Dangerous Things website. Lock manufacturers do not sell implants as the locks are meant to be used with cards or fobs.
The lock you will probably buy on amazon. An NFC or RFID standard lock. Check this out for lock-implant compatibility : Chip compatibility matrix - Google Sheets
If you’re talking about getting the implant installed you can ask a friend with medical experience or contact a piercer/ body mod shop in your area. Dangerous Things has a map of trusted places.
I assume you’re talking about your home door. Most NFC capable door locks will do the job. If I were you I would pick one mentioned here to be sure it works with the implant you will choose.
You setup the implant exactly the same way you setup an keyfob. The lock will come with instructions for that.
The NeXT is a good first implant. So you can get that and install a lock that is compatible with the NeXT from the list
The reason you see the NeXT twice in the list is because it works with two frequencies to be compatible with more systems.
You can also look at this for example:
The xNT is the same as the NeXT but with only the one frequency.