Trying to find a plugin to create a menu based on post tags

My client has a website with a portfolio built into his theme. When he tried to changed theme he realised his portfolio disappeared. So I have turned all of his galleries into pages, and portfolio items into posts, and created a post grid for him.

Now I am stuck – he used to have a little menu which contained all the ‘tags’ from within that gallery which simply filtered the results without leaving the page. I would very much like to replicate this filtering posts in the grid based on post tags.

~I have tried googling and several plugins but seem to be barking up the wrong tree, entering the wrong search terms. I do not want a custom menu of post titles. It has to be based on tags and preferably loads on the same page.

I don’t hold out much hope that anyone will answer this… but would be very grateful if someone would!