Shop for used
The only modern top break I know of is the Schofield replicas made in Italy to duplicate the 19th century Smith and Wesson product. It is now made in .45 Colt cal. Fairly expensive. Then there are some fairly recently made inexpensive .22's from NEF or H&R that are good plinking guns. Postwar top breaks include the H&R models made to fire .38 S&W(not "special") which is a lower powered cartridge in that size. Those were also used as guard guns for defense plants in WW2. You would have to go to a gun show or shop for used for all of these guns except the Schofield. Bear in mind that the top break is not a very strong design with modern ammo, but was fine with black powder cartridges. But it is plenty strong for the .22 or the 38S&W loaded to factory specs. You should look for any substantial looseness in the guns when the top is locked shut. No wiggly barrels or moving up and down. Also on the .22's watch out for chewed up ratchets on the rear of the extractor. Hard to get parts for these. I have a prewar H&R topbreak that I am still looking for a parts gun so I can put it back into service. Neat looking, but parts worn out. I also have a little 5 shot .32 H&R from early 20th. century that is excellent and I want to fire it one of these days with factory ammo. But most of the inexpensive ones you see will be rusty pieces of worn out junk. Antiques from before 1920 are around, but you would pay a good price for a gun good enough to shoot, or it might be too valuable to risk damage from much firing. Best bet is finding a good H&R type .22, economically.