Ken Null makes two inverted shoulder rigs - one with a pull-through snap and one with a "twist" snap break. Both are synthetic, and can hide under a tail-out button-front sport shirt, if sized loosely and of fairly heavy fabric.
Lou Alessi makes another of leather, with a fine harness and thumb break holster - ammo pouch on the off-side tie-down that will fit a speed strip with only five rounds in it. Both the Null and Alessi rigs are comfortable, if worn over a shirt with a collar, or a crew-neck T shirt. With a normal, lose-necked T shirt they tend to ride up and irritate. With an adjustment for that, both are good all day rigs.