Share 'Truss nut replacement for 80s Sigma DT-4 (Korean)'

Hi Hoping someone here might be able to help. Recently acquired a Made in Korea Sigma acoustic. 5mm truss nut is nearly rounded in the socket area so wanted to replace before using it further. The thread seems to be very close to 25 per inch (a M6x1.0 ‘seems’ to fit the nut for about seven full rotations then stops). M6 is pretty close to 1/4” but cannot seems to find 1/4 x 25 truss nuts, or M6x1…