Ive got <C> 74 -30t third rings, took them off my Race Triple to fit a 24t instead..

the period mix I use is a Rally RD for the capacity and chain wrap

there is also the possibility of a machine shop threading the Crank arm itself, to bolt onto..

Campagnolo did that themselves for their Triple, a less woos 36t .. [so probably only 2 lower ratios ]

I used a Gippiemme triple as a wide step Double , set it up as a 52 36.. 52 in the middle chainguard disc outer..