You really have only two choices. 1) watch the online auctions and flea markets, etc or 2) contact one of the 200 custom mold makers to have one made. There are a number of guys who cut molds with CNC operated lathes, instead of making cherries. Those machines can duplicate nearly anything
About a year ago, I saw a place advertising any mold for a bullet at $29.00. Send them a drawing or an actual bullet and they would do the mold.
My TC Catelogue (No 8) does not list a 32 cal Maxi. smallest being a .350 and going up to 54. My Mountain State Muzzleloading Supply catelogue from 1980 also only lists down to the 36 cal. I thought I remember a 32 being made, maybe I was wrong, perhaps rare as hen's teeth.
I see the same question come up every few months. Probably a custom mold maker is the only way.
I still have about a half dozen left that I bought at Fort Chambers Muzzleloader shop in Chambersburg. But I wanted to make my own. I guess I'll have to keep my eyes open. My T/C Systems One shoots them so well.