Can I still get a new cellular plan for my Apple Watch Series 5?

I wanted to know if I can still purchase a celluar plan for my Apple Watch Series 5. When I looked at Apple's main store site, all I found were plans built in to the new-generation watches, and I got a bit worried. I feel like certain providers might be able to help with this question, but I want to ask here first.

If the option is still available, are there any specific steps to set it up (e.g., should I use my phone to initiate the process, or should the watch just be connected to the internet)?

[Re-Titled by Moderator]