I have one you can have.   It is 1" wide , 3"long  and 1/8 inch thick which should be enough for both bow tips.  It is water buffalo.
Also have a chunk of cow horn that is almost 100 % flat. You would need to use a heat gun on it and a weight to get it completely flat.  Trouble is it is mostly white in color but a nice looking horn.
I have used them on a couple self bows and they look good.  Contact me ASAP as I leave to bait for bear in the morning.