WP theme authors no longer support or update, what are my next steps

I have two clients with a WordPress theme I bought from Themeforest. My client wants another site with the same theme. However the theme is no longer supported or updated. Client will not pay for a new theme on the existing sites. Meanwhile, PHP and Wordpress needs to be upgraded. I’m stuck.

Can I pay a developer to update the WordPress code of the theme?

Yes, you can hire someone to do this for you.
You can hire someone from here - https://studio.envato.com/