Is there any source of Themes for MU

There is no specific source for MU themes. Unless you are implementing special functionality yourself that needs to be treated in some special way by themes, there is no reason why all the normal themes wouldn’t work for you. Customizing themes is a whole other issue, one which certainly doesn’t belong in the multisite forum. Google for customize wordpress themes or try the Themes and templates section.

Yep, any regular wordpress theme will do.

Thank you ! I will try .