92190A143 Grade 5 Left Hand Hex Head Cap Screw, 1/2"-13 Coarse Thread, 2-1/2" Length, Fully Threaded
94280A119 Right Hand/Left Hand Threaded Coupling Nut, Grade 2 Zinc-Plated Steel, 1/2"-13 Thread Size, 4" L, 7/8" W
NOTE: They are english, not metric like the original. Good luck finding metric stuff.
I had to take a little less than 1/2" off each end of the turnbuckle to get it the same length of the other one.
Hope it holds up, the turnbuckle is only grade 2, bolt 5.