As far as patterns - you really don't need one! It's a rectangle with a casing with a cord threaded through it. The bag should finish about 1' larger all around than the intended deck so that you have room to slide it in and out, space to wrap the cards in a cloth, hold crystals, etc.
In most pattern books near the back there is usually a section of 'Accessories' and there may be elaborate reticules and purses there; also, if you are of the adventurous sort, check out the medieval women's patterns and see if one of the costumes has a bag to go with it; you may not want to spend $$$ on a pattern for one part of it, but there are always sales! {What I used to do is if I found a pattern and only wanted one part of it - take out the direction sheets and look at the sewing directions, memorize them, put them back in the pattern - and fake it when you get home!}
When I was designing period women's costumes I usually used the scraps from the costume to make them a matching reticule - so you don't need a lot of fabric. You can get four or more spacious tarot bags out of a single yard of any fabric.
My suggestion to you - my ambitious new sewer - is to learn to use the buttonhole attachment. I always made my bags with double laces so they would open and more truthfully -close- more easily since the friction keeps the top closed. Once you make the casing for the cord, make a buttonhole , one on each side BEFORE you sew the casing down! Sew casing into place. Take one piece of cord and thread through right side hole, by-pass the left hole and bring the end out the hole you started and tie ends together. Do the same through the other hole. Now, pull the two knots and the bag will close ever so gently and beautifully. To open, just insert your fingers into the 'purse' and gently pull the opening apart.