Hi There!
I see you are looking to get your Magento extension customized for checkout, I will be a good fit for your job as I have hands on experience in development and customization of extensions for PHP and related CMS like: WordPress, Magento, Joomla, Drupal etc.
We can discuss more on the same over a call if it sounds good.
Looking forward to hear from you and working on your job,
Regards,
Gagan