In a pinch I used the LH threaded "rod" that came on a turnbuckle--one of my old garden tractors has a LH thread nut to hold one front tire on,that threads into the spindle..not knowing it was LH thread,I twisted it off...
I found the turnbuckle at Lowes and I just cut the "eye" end off it and welded a nut to it...
The guy in the hardware section of Lowes said "We used to have a drawer with some LH thread bolts,but didn't re-order any because they were such slow sellers.."..so maybe a "good" old fashioned store might still carry some LH stuff..