If you search Ebay for Winchester Bowie there are always a bunch of them on there. Basic decent quality basic Stainless Steel.
They are made for Gerber Knives. Some of the earlier ones are U.S. made and now are made in China. Shop around.
Or if you are feeling creative - you can search Ebay for DAMASCUS Bowie Blank. There are some very decent Damascus blanks listed on there these days.
Damascus being very labor intensive to produce most are coming from places were labor is still cheap but, the quality is there and the prices are VERY reasonable.
I remember when U.S. Made layered Damascus was selling for 50 to 100 dollars per INCH of blade.
Now you can get a very good large Damascus Bowie Blank import for around $30.00 and up.