I know Unity is primarily a 3d system, but if you are in need of some 2d rendered isometric character / monster sprites here are some I rendered, which are freely available either for commercial or non-commercial use.
They are all animated, with a good number of frames. They require a program, which I’ve included to convert the images from my own format into either TGA (with alpha) or BMP (with mask colour) when exporting.
A range of frames can be selected to export, or the entire sprite’s frames. Sprites can be flipped horizontally - most of them come in 5 directions (of 8) and the 3 left facing ones can be flipped to generate the other 3 right facing images.
As an example here is a picture of one of them:
