From what I can gauge, Trackmania Original is a free add-on to the actual original, on a wiki it states "Whatever the version of TrackMania Original you have, you can always download and install the lastest one for free." I would assume the one you were trying to download was
here, as it leads to a 404 as you stated. I do not believe you can actually download the actual original through normal means, namely because it is not abandonware. I think your best bet is to buy online, however
$40 dollars on Amazon - $4 dollars on Amazon
I don't know which one is which, the difference between the two, or which one is the one you're looking for. I don't know much about the Trackmania series as a whole, but wow did these early ones have odd naming conventions.
Hoped this helped a bit on how you'd take action on getting the game at least.