Hi,

The module Helpdesk is available for Odoo Enterprise Edition, It is not available for the community edition. And you have no direct access to the enterprise GitHub to get the helpdesk module.If you need to get the helpdesk module in the community edition without switching to enterprise, you need to create custom modules with your requirements. Or you can check the odoo apps store to get similar modules which are available for the community

Hope it helps

No, only odoo partners get access to the source code of enterprise modules.

Even if you somehow manage to get the code, your database will expire 30 days without enterprise subscription.