Can you buy a conversion kit to change a Baikal IZH-18MH 223 rifle to a 12 gauge single shot gun?

No, you cannot buy a conversion kit to change a Baikal IZH-18MH .223 rifle into a 12-gauge single-shot shotgun. These firearms are designed with different calibers and operating mechanisms, and converting one to another would not be feasible or safe. Additionally, such modifications could violate firearm regulations and laws. It's best to purchase a shotgun specifically designed for 12-gauge ammunition.