Got hay?
Get a hardwood closet rod and cut a long slot in it. Keep in mind that perhaps no one has ever made a hay rake handle that's "too long"!
My closet rod wood turned out to be impossible to steam or boil bend sufficiently for the large span I desired without cracking. (I think the closet rod was labeled as hemlock) so I discarded my practice rod and...
Tie a wire near the end of the slot and 3D print some curved forms. I made my forms out of orange ABS. They don't have to be orange.

I used two forms per split handle arm. My 3D printer couldn't print a single form of sufficient length, but it turned out to be a blessing to use shorter forms when pounding the forms on and off of the dowel arms.
Oh yeah--make your rake head from hardwood dowels and lumber too.
If you drill the head lumber from both sides, you can actually benefit from the almost inevitable slight mismatch where the through hole halves join mid depth, because the mismatch will help to make the press fit of the teeth dowels. No glue required! (I learned this trick from a website describing how people nailed wooden structures together with wooden pins rather than metal nails back in "the old days".) Use water as a lube when hammering the teeth into position.
I boiled the split handle ends in an extra long extended stainless "mud pan" for about an hour. I made my extended pan from two normal pans by cutting the ends off the pans and bonding the pans together with high-temp silicone RTV sealant.
Pound the forms onto the ends very quickly after a good steaming or boiling to minimize cooling. Boil with the wire tie already installed. I let my handle sit to cool and dry for a couple of days during last year's hot summer before I drove the forms off, one at a time.
A large rubber mallet works well for driving the forms on and off the handle.
Carve and sand the split handle ends and drill the holes into the head for a tight press-fit. If you get it just right, you'll not need glue or nails here either.
Rake up some hay!
I used this design as a starting guide but my rake is larger and I used straight teeth, which I think work best for raking hay into windrows. Perhaps the angled teeth work better for lifting and turning the hay.
https://www.motherearthnews.com/diy/hay-rake-zmaz79mjzraw