Hi Himavanth,
In HR, your employees would have been created as Vendor.
So If you need to use them in Sales, you need to create corresponding Customers also and in Link those Customer and Vendors for Employees.
Assign External Number Range.
About, Tracking of Promotional Items and Physician Samples, I will suggest you to use Consignment Process.
That will give you exact control that to which Employee you have given how much Material and when he distributes or in your case consume that Material, show in system Consignment Issue with Zero value to that Employee.
Yes, you will have to create 500 Sales Order. And I will suggest you to do the same for better tracking of stock.
Another way is to Use One time Customer for Group of Employees and just link Exact Customer Code in Header Partner function as Employee (Here you can use HR Masters... Suggesting you to Test first before proposing to Client)
Regards,
MJ.