I have a super cheap one off ebay, it’s got tons of play in it but it’s really simple to work with anyway (you don’t need the tool to have no play, you just need some consistency)
You can go right back to basics… Mech bolt thread is hte same as a QR axle, so, if you’ve got one of those or an old wheel you can thread it in and you have a perfect perpendicular sticky out thing. Put a straight edge through the dropouts- I used a bit of spare threaded bar- and you can easily see if they’re parallel, and the axle now makes a really good bending tool. Doesn’t work in designs that need the wheel in to secure the hanger though.