Your $100 Lewis v. Tua is probably the lowest minted chip for an actual fight. I have seen at least three boxing non-fight LEs issued with a mintage of 50 - the three $25 Palace Station chips come to mind (Barkley, Mercer & Rosenblatt).

The lowest mintage on a boxing chip I have seen is the chip below with a mintage of only 15:

I believe Las Vegas now has rules in place that will not allow casinos to make these small mintages. I believe the minimum is now 500, but I am not positive.