It shouldn't be too hard to draft your own pattern. Lay your BS on its side on a piece of paper and trace around the outline. Add a bit more for ease and seam allowance. The middle piece is just a long rectangle. You can make the handle hole and slit out of one piece and run seam binding around it. In the 1st example I linked to below, it looks like she did a satin stitch around the hole and did a fabric self binding on the slit. IMHO seam binding is easier.
https://www.etsy.com/listing/1048523...ref=listing-17
Sizzix Big Shot Dust Cover Quilted Free Red Fabric with Polka Ribbon | eBay
You could use velcro to close it (see second link - you have to scroll down to see it).
For the middle piece, you can give yourself wiggle room by cutting your rectangle extra length and marking the middle, Match the centers of the side pieces to the middle of the rectangle and pin it together. Slip it inside out over your BS to make any adjustments. Sew and trim the excess fabric from the end pieces, leaving a hem allowance. Or trim it exactly and use a fabric strip or seam binding, if you are more ambitious.
I would use pre - quilted fabric. I just made a cover for my Zing e-cutter from some and I think it gives a bit of extra protection from both dust and dings. Plus it has more body so it holds it shape better than just plain fabric.
BTW - I had never thought about a cover for my BS and now I'm inspired. Thanks!