There are a few more seats available not listed here.
Solo seat: Standard bicycle seats have a 7/8″=22.2 mm clamp. Some 24-35 mm moped seat poles have a 22.2 mm top section. Those can accept standard bicycle seats. Other moped seat poles are a straight 24-26 all the way, too big for a bike seat clamp.
4904 beach cruiser bicycle seat w/springs $22
10.5 by 10.5 inch, dual coil spring suspension
fits any moped with a 7/8″ seat pole top end
seat single Peugeot new with 1″ post $45 fits Peugeot 103 and others with 1″ hole