Upvote:4
The coat of arms of Guillem de Clermont-Lodève, ancestor of Tristan of Clermont, is described in Documens historiques et généalogiques sur les familles et les hommes remarquables du Rouergue (Vol. 1, page 538) as "fascé d'or et de gueules de six pièces et un chef d'hermines". This coat of arms would have been inherited by Tristan, and is very similar to the one borne by the Archbishop of Narbonne referred to in andy256's answer. It omits the religious symbology, however, and the field is divided into six, rather than four.
A representation is available on the Wikipedia Commons:
Upvote:7
The Catherine of Taranto article you mention refers to the Orsini article, which shows the Orsini coat of arms:
See the references and links at the bottom of the page.
Rely on the sources rather than Wikipedia in this case.
Update: This article on François Guillaume de Castelnau de Clermont-Lodève, Archbishop of Narbonne, appears relevant. He was born in 1480, 50 years after Tristan's death; the central part of the coat of arms may not have changed. But all this is supposition, included because you wanted leads.
Note the galero in the image: