You mean the old baking pan with the lip?

Lodge Pre-Seasoned Cast Iron Baking Pan with Loop Handles, 14", Black https://www.amazon.com/dp/B0000E2V3X/ref=cm_sw_r_cp_api_glt_fabc_8SZKXWHH7GK4MQHZR9GW

Baking steel or cast iron pizza pan. You will be a lot happier spending that extra cash and getting a better result.

I'll probably buy one of these

where can I get something a bit bigger though..

Hi.

I have the heat deflector and I use a pizza steel on the grill. This one fits just about perfectly - https://www.amazon.com/gp/product/B0000E2V3X

I normally don't use the heat deflector as the pizza steel does a good job of providing even heat to the pizza. You could get by without a pizza stone / steel, but you will probably have some issue with the grates. I would think that the grates would allow some of the dough to go in between them and give you an interesting washboard design on the bottom of the pizza. I would absolutely make sure that the grill is greased and maybe try with just a dough or with very little toppings to see how things go.

Edit: My deflector is the one over the charcoal down low. Use the grate, or use the grate with a pizza stone. My heat deflector looks like this - https://www.amazon.com/Hongso-CR-18-2-Smokin-Char-Griller-Deflector/dp/B079HS3DJ7/ but it's the Char Broil original one.

Edit 2: This is the one I have - https://www.amazon.com/Char-Griller-6201-Smokin-Stone/dp/B009E8NATC/r.