Most common way to get info about a domain is to use WHOIS to query the databases that store the registered users of domains. But there is an option for people that register new domains to hide their info and that's the case for theresia.name and as long they don't have a contact form it's hard to tell how they could be contacted.
If not written in English, try native language. And the best way to find is the useful links. http://www.theresia.name/de/slinks.html
Just replace (at) by @, and you have a mail. I discovered his mail there, with confirmation by thanks to Google translation.
Administrateur du catalogue, référent de nombreuses nations antiques et de la Lorraine.
Catalogue administrator, numerous Antique nations and Lorraine referee.
This is the problem with wysiwyg website creators. Emails will bounce back by postmaster if the address is invalid, it gives random reasons by default. www.theresia.com is showing as under construction from a German company. So as a guess, I would say this is the new domain they are moving to.
Using the Whois for the .com domain shows contact info email address which I have now sent a message to enquiring if they are the same person for both sites. I might as well find out and try a few variants to see if I can get any success finding the web master of theresia.name for you. No point giving you random emails to try without success.
If it is the same person for both domains, then job done. If not, then I will keep hunting.
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