I've been doing quite a bit of research into this for my own Neapolitan army project
I have plenty of info on uniforms and regiments for the nations in question but less so on the flags. Piedmont is ok, some on Modena, very little on Naples at all.
I've made a downloadable folio up with links to various sites and some articles on my Blog which you can see on my profile - look for the tag "WAS Italy".
if you come across any info, please so share!!