This is a great project for someone who likes to make their own tools.  It's a wooden mortise gauge with a thumbscrew to lock the distance between the pins and a wedge to lock the fence.

Project hardware links:

Sketchup drawing

http://simplecove.com/assets/files/ef8aee7b-5043-4645-b978-18fa5003b993.skp

Music wire

https://www.amazon.com/Small-Diameter-Music-Wire-Asst/dp/B001J6AHCA/ref=sr_1_1?ie=UTF8&qid=1498774773&sr=8-1&keywords=music+wire+assortment

Brass thumbscrews

http://www.homedepot.com/p/Crown-Bolt-10-24-x-1-in-Brass-Knurled-Screw-2-Pack-99228/203537777?