Search “IPS Crankarm Set” on eBay and you’ll get some returns for the Lasco Independent Pedaling System tandem cranksets with a freewheel in each set. You can use just one set, but if you use two, both riders can coast independently. Right side timing chain is required whether you use one or two cranksets. We ride a da Vinci tandem, but used this setup to convert a Santana Sovereign to independent pedaling/coasting and it worked well once we sorted out the proper bottom bracket axle lengths. They use square taper BB’s. Similar, if not the same, cranksets were used on ATP Vision and Sun recumbent tandems.