The quivers that are custom designed to fit the TAC15
/15i crossbow were made by a company called New Dawn out of either North Carolina or Virginia. The New Dawn Quiver was produced for Vertical compound bows and was rated as probably the best quiver made in the industry.
The bracket that adapted it to the weaver rail of the TAC15 was custom produced by Super 91 in a machine shop. The combination of these two items was packaged and I believe that Len Backus has contractual rights as the sole distributor in the US. I'm not sure if they are still being made or not, but I own two of them and use them on both my Mathews Compound bow and my PSE TAC15i.
I highly recommend them, if you can still get one. They are made incredibly well and are indestructible, so they will last forever and are problem free. Once you see how easily they go on and come off you'll never use anything else.