I have an old lotus ive been overhauling with SR super custom cranks (170's). I rode the bike for a bit with the left crank loose, and I think its now too worn to really warrant putting it back on. It rides ok if I do, but slowly loosens again over time, and I dont think lock tighting the bolt would be the best idea. The rest of the bike is 600EX arabesque components.

Ideally id just like to replace the left crank arm as the crankset and chainrings and whatnot are in perfect condition, but its hard to find an SR crankset these days. What can I replace this with? Should I just get a used crankset, and what would be my cheapest option?