I have used this grill for 11 years. The firebox collapsed, so I either had to repair it or buy a new grill. I decided on the former, because I could overhaul it much cheaper.
Getting an exact replacement for this is not possible. It’s no longer made. The Large BGE firebox would probably work, but I went another direction....
My new firebox choice- the new sectional Kamado Joe firebox.... https://www.bbqguys.com/kamado-joe/classic-multi-piece-firebox-kj-mpfb23
This caused a second issue- the fire ring is too tall. It is about 6” tall, that is 2” too tall. So I bought the Kamado Joe Classic fire ring, it. Fixes the problem. About $65 delivered.
I could have stopped there, but I continued....
Cheap upgrades... (everyone should consider these)....
new bottom grate... Do this! https://www.amazon.com/gp/product/B01N4EPPX6/ref=ppx_yo_dt_b_asin_title_o04_s01?ie=UTF8&psc=1
more expensive other things....
kick ash basket... Do this! https://www.amazon.com/gp/product/B07C9XJ28J/ref=ppx_yo_dt_b_asin_title_o04_s01?ie=UTF8&psc=1
new side tables https://www.amazon.com/gp/product/B017O7JNB8/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1
kamado joe classic joe divide and conquer system
new cast iron grill grate https://www.amazon.com/gp/product/B07CZHZWDM/ref=ppx_yo_dt_b_asin_title_o04_s01?ie=UTF8&psc=1
grill expander https://www.amazon.com/gp/product/B06XTL6SZQ/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
what I have found....
this grill now works far better than it ever did. It gets hotter, starts quicker, is more consistent in temps. This all due to improved airflow, mostly due to the new bottom grate and the ash basket. It is easier to clean as well.