Same here.
To the OP and everyone looking. It may be easier to find the regular Mt Dew in the 20oz bottles with the Xbox logo. Check convenience stores, gas stations, etc. It’s not the cheapest route, but those tend to turn over faster than packs in supermarkets.
100pts per bottle, you need 6 for the mount.
You can only submit 5 Mt Dew codes per day, regardless of of which type/packaged size you purchase and the “per day” ends at 11:59ET
You can additionally submit 5 Doritos codes and 5 Rockstar Energy drinks codes for a total of 15 codes per day, but limited to 5 ea from the three products. Mt Dew, Doritos, Rockstar.