one of auctiva's community members, magie, wrote a good guide for intro to template making
https://community.auctiva.com/eve/forums/a/tpc/f/6881044121/m/1251067521 free templates - there's some places on web to get them, many are shared member to member here, etc. all would require tweeking to make auctiva compatible (unless the donor has already done so). basically this consists of adding auctiva tags where needed (the tag for where to put the image, where to put the description, etc)
here's one site with free ones that would need tweeking for auctiva
http://auctionsupplies.com/templates/ another page that also has mepage templates
http://www.xample.net/templates.htm and of course you can modify auctiva's templates to suit your fancy. (change colors, etc) and create an individual look pretty easily.