I buy 2" x 2" blanks from home depot or Lowes. They typically will carry Oak and Poplar in 3 foot lengths. Poplar is easier to turn on the lathe than oak.

Something like this: https://www.amazon.com/HELYZQ-Super-Rectangular-Silicone-Rectangle/dp/B08XM6L61B?th=1

Then get a rectangular silicone mold that is 2" wide (same width as your lumber). I don't know if this is the right size - I just found a generic rectangular mold to give you an idea of what you're looking for: https://www.amazon.com/HELYZQ-Super-Rectangular-Silicone-Rectangle/dp/B08XM6L61B?th=1

Once you have your mold, figure out how long your mold is. Mine is 6 inches long. Cut a length off your board that is slightly shorter than your mold. I typically will cut a piece of 2 x 2 that is 5.25 to 5.5 inches. Then cut it on a wavy line through the middle so you have a roughly 2.5" chunk on one end of the mold, a 2.5" chunk on the other end, with a gap in the middle. Fill the gap with colored epoxy. Then when it sets up, you have a wood/epoxy blank that you can turn into a nice Christmas ornament.

This is the dye I use to color my resin: https://www.amazon.com/gp/product/B08DHDGP24/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1