Welcome to the nut house. To be sure we are on the same page, there really aren’t many “bonsai” available online. Finished bonsai are also very expensive.
You are maybe looking for pre-bonsai - something to grow into bonsai? Some of my go to are (1) kaede-en for smaller seedlings; (2) international bonsai for great starter material, (3) green thumb bonsai for field grown trees; and (4) Brussels bonsai for specimen pre bonsai. I haven’t had the opportunity to order from them yet, but wiggerts has great trees as well. So does Bella bonsai. You can also find folks here selling stuff, many times at better prices.