Following a link from the Duke4 forums, I arrived at this site:
http://wolfmap.ru/forum/viewtopic.php?f ... 0b32bbee35It's a thread that has conversions of a number of models from a variety of games to the MD3 format (making adapting them to GZDoom relatively easy).
The forum is in Russian but it's pretty clear what it's all about even if you don't speak Russian. Most of the models have preview pictures and the "DOWNLOAD" links are obvious.
The range of models includes statues from TES games, WWII tanks and artillery, industrial machinery, other vehicles, food and various bits and pieces. They are almost all non-animated map objects (the exceptions being animated dragon flies and butterflies IIRC).

To download the models you need to log in to 4shared (either via facebook, google+ or with your own 4shared account) but the downloads check out and there is some nice stuff there. Some of the models seem to be from games that support higher poly counts than the MD3 format. I say that because a few of the models have been broken up into separate sub-models. However, GZDoom can handle that just fine by using multiple models per actor anyway.
I think that I have managed to download all the files and if anyone can suggest somewhere sensible to upload them, I can do so. A zip of them all comes to 36MB. This would be a more convenient way to get them than visiting every single link (like I did), waiting 20 seconds and then downloading and extracting.
As ever, I recommend Noesis for a nice quick way to browse and view the models.
http://www.richwhitehouse.com/index.php ... hp#prjmp91