You could repurpose an air cleaner box from a Mitsubishi Chariot/Colt Vista wagon/Expo. I had to find a replacement but getting the factory round one for a gen 1 was near impossible. The air cleaner boxes from the models I've listed are oval and will swap with the stock box with a bit of tweaking - but if you're looking for a sacrificial unit to adapt to a Weber it would be a reasonable box to start with due to the larger air filter surface area and box volume.