I've bought wood from these guys before. It's pricey but always top quality - https://www.woodworkerssource.com/search.html?Search=spanish+cedar
It's been a while but I remember having to call if I wanted details on widths. Looks like they have 1/4 inch stock but anything else will likely require a planer and/or bandsaw to get thin.
There's also random stuff on Amazon that might work for you like this