There are very few images of the mission era Franciscan friars. Remember that they lived well before the advent of photograph. If an image survived it had to be painted or drawn as was done with Fr. Junipero Serra when he was in Mexico City for a visit.
I can tell you a few things about Jose Cavaller. When the missionaries left Spain they were described in their passport records. Fr. Cavaller was described as of medium height, somewhat corpulent (i.e. he was a little on the fat side) and of a dark complexion. He was placed in sole charge of the new mission of San Luis Obispo at the age of only thirty-two, so he must have impressed the Father President. The mission was very successful under his leadership. Only four years later, in 1776. it was self sufficient;
If you really need an image you will have to draw what you think he looked like from the brief description I have given you. If you do, send me a copy.