Dreamweaver

"but there are serious compatibility issues."

LIke what for example?  Code is code.  If the code is valid, it should work in the latest version of DW.   Although the reverse might not be true.  Modern code isn't always recognized by outdated editors. 

Adobe hasn't sold or supported any Creative Suite version of DW for some time. They also no longer do platform swaps or license transfers. That being said, there's no legitimate way to obtain the old software anymore, though it can still be found online through various, and highly suspect, sources.

The chances of getting a true copy of CS4-CS6 without it being a scam are incredibly low.

There are a number of fake "Adobe_Firstname_Lastname" accounts on this site who will likely send you a private message that they are Adobe Support and can sell you CS6. They're just scammers out to get as much of your personal information as they possibly can.

Unfortunately Nancy is right, albeit a bit blunt. You will probably spend less time and effort rebuilding your site to modern standards, with a modern editor, than you would repairing your credit after falling for one of the many, many scams online surrounding the purchase of legacy software.

It's 2020.  Your 13 year old website is outdated.  Even if you could find it, old software won't fix that problem.  Roll up your sleeves and get to work on a new site with modern code and responsive layout that is mobile and tablet friendly.  These days, anything less is unacceptable.

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Beware of fake Adobe reps offering to sell you software or take control of your computer.  It's a scam.  Run away!