We don't have a FTP server of our own, this is sourceforge. And yes, it fails pretty often. It seems like some of their mirrors are out of sync (the 404 error means they don't have the file you're requesting). You can try to get the files manually here.
Are you located in france? Another french user had the same problem.
Viech: This may answer your question:
If i remember correctly, you host/manage the quake.fr server?
No I don't. I do manage the Map Test Server but I don't know how the vserver will react to a high bandwidth consumption. It has a 100 mbit/s connection but that is probably restricted to some definition of "fair use" and will get throttled if you stress it too hard. It could also have a negative impact on the game server performance. If we manage to set up a load balancer or choose downloads randomly from a mirrorlist, I could contribute some bandwidth though.
root@game:/var/games/unvanquished/main# curl --retry 5 -fLo /var/games/unvanquished/main/map-parpax-d01.pk3 http://freefr.dl.sourceforge.net/project/unvanquished/Assets/map-parpax-d01.pk3
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 44.8M 100 44.8M 0 0 104M 0 --:--:-- --:--:-- --:--:-- 104M
I have the same problem in France, it is a quite strange.
I will replace the asset manually when I have the time.
ps : It is a little out of the subject but have you a link to the assets on blender format ?