Windows 2003 R2 to Windows 2012 R2

It's been a while since I have been on this site. But, I need some help on this one. I have inherited a network that consists of a Windows 2003 R2 server Domain Controller, a Windows 2012 R2 server Domain Controller, and a Windows 2019 server that is not a domain controller, it is an RDP server. My problem is trying to decommission the old 2003 R2 server. Unfortunately there is no sysvol or netlogon shares on the 2012 server. So, I cannot retire it without losing Active Directory. The only thing I can think of is to bring a windows 2008R2 server into the domain to sync AD with FRS then upgrade it to DFSR. I'm pretty sure once I do that I can retire the 2003 R2 server. But that leaves me with another dilemma. That is I do not have a copy of 2008. I looked online and on ebay and I cannot find a copy for a fair price. Most want over $1000.00 and go up to $2000.00. I can find just the install disk, but have no key to activate it. 

IF anyone has any ideas, please let me know.

Thank you

Doug