I don't know where I found this, but it's what I use when making tacos. I don't buy the packets of seasoning. All the ingredients are dry (not fresh).
Also, please note there is not any salt in this recipe. If you are used to store bought taco seasoning you will probably want to add salt.
6 tsp chili powder
5 tsp paprika
4 1/2 tsp cumin
3 tsp onion powder
2 1/2 tsp garlic powder
1/8 tsp cayenne pepper
I put all of this in a zippered bag and shake to mix.
7 tsp of the mixture is equivalent to a 1.25 oz packet of seasoning (used for 1 lb of meat). This recipe will make 3 packets.
I've always just stored my bag with the seasonings in the cupboard with my other spices, but it would probably stay longer in the freezer (as all spices do - per my MIL).