There is none. Other than upgrading, your options are to save in some other 3D format - eg, 3DS - and assign all materials manually in Artlantis 1, or to back-save to ArchiCAD 10, the last version capable of saving in Artlantis 1 format.
The plug-ins are developed by Abvent, with updates on their web site, but also bundled for our convenience by Graphisoft. Any questions about the add-ons, why they no longer support version 1, etc belong on the Abent Artlantis import plug-in forum:
http://www.artlantis.com/index.php?page=support/forum/liste&fid=atl_import_us
Sorry there is nothing easy. No problem with versions 2 and 3 of course, but the upgrade specials that Abvent offered to 1 and earlier users have expired as far as I know.
Cheers,
Karl
PS Do note that there is a 1.2.6 version download on the Abvent web site. I cannot remember if that was a free upgrade for 1.0 / 1.1 users.
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