I do have a few references to tomahawks being thrown in a combat situation, not for a knife, though.
Doddridge: "The Indian then threw his tomahawk at his head but missed him;..."
The South-Carolina GAZETTE
September 13, 1760
CHARLES-TOWN
"At day light Mr. Miln, with the ***** Abram, went in pursuit of the deserter as far as Twelve-mile river; but not overtaking him there, returned; and as they were crossing Crow-Creek, which is very near the fort, they were fired at by three Indians, who shot one of Abram's boots through and his horse under him, and as he fell threw a tomahawk which struck him on the back; Mr. Miln and Abram however luckily got back here: A party immediately went out, but the enemy surpassed them so much in activity, that they soon disappeared, and the party bro't in no other trophy than the tomahawk which had been thrown at Abram, and some horse flesh."
From Spencer Records memoir, _Pioneer Experiences in Pennsylvania, Kentucky, Ohio and Indiana_.
“They then sprung towards the old lady, one of them threw his tomahawk, and stuck it in a tree near her head: she however stuck to her saddle, and her horse soon carried her safe home.”
_Frontier Memories_, interview of Col. John Graves, 1786:
"Everyone was killed but one, who ran within 10 steps of me. Leaving blanket, moccasins and all, I threw my tomahawk at him. Next morning we looked, but if he was wounded we couldn’t see any trail of blood. All nineteen lay there in death."
_Frontier Memories_, interview of Sarah Graham:
" ... when she seen the dogs. She was so glad she jumped up run before the men were in sight. An Indian threw his tomahawk at her..."
Secondary source:
From _A History of the Daniel Boone National Forest, 1770-1970_, by the U.S. Prk service:
"When Jemima Boone and the other girls were rescued from the Shawnee, one of them threw his tomahawk at Jemima but missed."
Spence