If you are looking for a St. Patrick's Day gift your cat or dog, this page should help! These Irish Pet Costumes are Purrfect for St. Patrick's Day!
Top rated reviews: if Amazon has something similar with many reviews and 4 or 5 star ratings, that is likely to be a hit!
There appear to be no costumes for St. Paddy's day dedicated to cats, but the small dog sizes are said to work.
This link takes you to Amazon's top St. Patrick's Day gifts for men.