Any of the SRAM, Wipperman, even KMC chains in 3/32“ width will work well with the non-Ultra Suntour freewheels. SRAM PC-58, which I think has been rebranded PC-870, is what I'm using. With the Ultra freewheel I have, it's somewhat sensitive to width. Never had trouble with the original Sedisport, but the SRAM replacement does have a bit of ”hitch“ that I can feel intermittently. Functions fine, but I actually think it's the removable link catching a bit on the adjacent tooth of larger sprocket when in center cog (7-speed). Can't repeat it with bike in stand, and it also disappears when I'm pushing hard -- ”cruise“ is where I feel it. I've been meaning to try removing the removable link; but it's too darn convenient for simply removing the chain to clean it. Don't quote me, but Wipperman may be a tad narrower chain, as well as more expensive; you might check that out.

Occasionally NOS Sedisports appear on eBay; that's another option if you don't mind breaking the chain by pushing pins.