SHIM MAKING
After a bit of searching I found a hardware store nearby that sold maple veneer for about 7 bucks for an 8ft roll.
Maple Veneer:
https://i.imgur.com/tFMHvsPl.jpg
First I traced the neck heel onto a piece of paper to create a stencil. I transferred the outline to the veneer and started cutting. The veneer is really easy to work with. Cut very well with scissors and was kinda fun so I ended up making a bunch while watching a movie. After cutting I needed to sand the sides a bit for a perfect fit, but all in all it was simple and fun.
Making template:
https://i.imgur.com/5FrPxigl.jpg
I assume I will need to glue two or three of these things together to get the thickness I need, so I cut them in alternate directions of the grain. Which I think is the right thing to do...
Still need to shape the top of the shim that protrudes from the pocket, but they are basically done.
semi-completed Shims:
https://i.imgur.com/aj6W6B8l.jpg
@pablopepper gave some advice on how to come up with a tapered shim without many tools. And I might go that route.
HIS ADVICE:
But I am wondering if there is any disadvantage to simply using a flat shim.
I googled around and can't seem to find any reason a flat shim is a bad idea, but if anyone here has an opinion, I'd love to hear it.
Thanks!