Heh. I imagined these existing about 6 months ago and just made one ad-hoc out of printer paper.
I measured my tip and made a straight line in photoshop that was 1mm larger than the tip of my cue created, for me that was a 13.5mm line. I built a 'ruler' of hash markings along the line to the 'contact point' on the ball. Then I put a half ball semi-circle at the 'contact point and continued the line through the 'ball' printed on the paper. Then I printed a second paper with just the line giving upwards of an 18" stroke legnth.
Taped them together and voila, taped it to my dining room table which is exactly 30" off the ground. Not exciting or even fun, but a few hours a night with that when I couldn't go to the pool hall really helped straighten out my stroke, practice getting a good stance, and aligning the shot. It was very easy to see if I was on center or not by seeing the 1/2mm on either side of my shaft and the chalk mark on the paper after follow through.
It's not perfect, doesn't have the height of the ball, for dead center on both axis, but some cardboard or foam board cut to create the same thing wouldn't be that difficult.
I can remake the template and share it if you want, it's nothing special, just two pieces of pritner paper, and I've been meaning to remake it anyway with some 'upgrades,' possibly a 'pop-up' cue ball effect like in the Ouschan video. The hall I shoot at is an hour away, so any type of practice I can get at home is welcome.