It is very difficult to buy seeds online this Spring, because people have panicked about food this pandemic. You can try, but I don't know how fast you can get seeds.

Baker Creek Heirloom Peppers, rareseeds.com, look here for ideas.

They sell.... 'Ajvarski' is great, much better than bell peppers. 'Etiuda', a large Polish bell which is well spoken about. They also have 'Quadrato' yellow or red, 'Doux D' Espagne' a famous large long bell, 'Ozark Giant Red', and one called the 'Yellow Monster'.

If you looking for hybrids, try larger vendors like Burpee, but I doubt you will find many places shipping out quickly.

best to just to buy seeds locally at the store chains.

i also recommend not growing bells ;) but rather the long style peppers like marconi, corno de toro, costa rican, etc. they taste way better than bells and are typically less fussy growing than bells..