Just an idea but why not try to ask guys who created those units about exporting animations to higher resolution? Sprites were surely made form 3d animated models so it shouldn't be much of a problem for them. I know nothing about Civ3 community but I can ask those guys if you point me to a thread where you found a unit. Many of them maybe out of business now but I think its worth a try. They're all moders like us so I'm sure they'll understand why we're asking about it. Units are IMHO the most important part and we'd be aiming for the top quality.