Four misunderstandings in your post:
1. Antivirus programs protect your PC against viruses. They have nothing to do with the communication with your customers.
2. Windows 10 already has an antivirus program (called Windows Defender), so there is no real need to install one yourself.
3. You don't need a support number to install one, if you want to install one. Just visit the site of the maker of your preferred antivirus, pay if it's a paid one, download it and install as instructed.
4. A local number is just as good (or just as bad) as a non-local one for remote support. You only need local support if you want them to visit your office.
I have purchased a new personal computer for my Garments business in Los Angeles. I want to install an Anti-virus application for secure communication with my clients. Suggest me a valid Windows 10 support number for Los Angeles.