A good start would be a Webley & Scott Model 700. It is a relative modern BLE gun, has proven reasonably durable, has typical game gun handling, and is generally available in high condition for reasonable money. You could go to Holt's or Bonham's auction sites, go to the archives and search "W&S 700" to see recent auction gun configurations and realized prices. Be sure you understand whether the buyer's premium is shown in the price or not. Also, note that import to the USA will cost a substantial additional amount. You might also commission Dig Hadoke (a generally all-around good dude) to find you a suitable gun. If you are OK with a vintage gun (I sure am), pre 1899, Toby Barclay is also a very fine resource.
DDA