Check online police supply shops. You can get jackets/coats with side zippers at 9 and 3 o'clock from the hem up to the waist to create a slit for this purpose. Unzip it and tuck it around the holstered gun. I saw a midweight jacket being blown out at an online shop for ~$30 about six months ago, reg. $150, so there are some deals out there. I think it was a 5.11. Another option would be to have a zipper or velcro added to one you already have.
I have a light to medium weight 5.11 jacket with all those zippers everywhere. I am not a big 5.11 fan but they do have some things that are good. I love my jacket and definitely would recommend it. I think it would fit your needs.
Daniel