Here's a bit of a solution you can make that tastes similar!

Buy some regular or caffeine-free Pepsi

Go to a Taco Bell that has Mountain Dew Baja Blast, buy a big cup of it (without ice so it's not dilluted)

Mix it with the Pepsi (I recommend a mixture of 3 parts Baja Blast to 2 parts Pepsi, but experiment until you get a close-enough taste).

There ya go! It's fairly close at least if you get it right. Best we can do unless Pepsi will be nice enough to bring it back someday (which will take some bugging on our part of course). Enjoy!

......Just dropping in Skittles might work too, haven't tried yet.