I did a quick search for Saint (St.) on the STA website. These are the results that seemed the most likely to be applicable:

Name of Tartan ITI Number

St. Andrews 5899
St. Christopher 6778
St. Clement of Rome School 6742
St. Columba (one green) 2383
St. Columba (two greens) 3219
St. Eloi 5306
St. Francis Xavier University 5305
St. Giles Cathedral 3220
St. Giles Check 387
St. Kilda 1189
St. Patrick 945
St. Piran Dress 1685

I understand that not all of these are necessarily connected with the Catholic Church, but they at least provide a starting point. Perhaps Matt Newsome could be persuaded to weigh in. His theological and scholarly leanings might make him the perfect resource...

Cordially,
David