You can get them on Aliexpress here: https://ali.ski/3GV0K
Just be sure to choose the right set for you carefully, more details below.
And now more about each of the available things.
Sets of stands and pins with bonus postcard. You can't buy card separately, only together with the set.
Note that sets are slightly different. There is a set where all items are only with Noelle or only with Diluc, and there are sets where there is a Noelle standy and a Diluc badge and vice versa.
KFC Genshin Impact set with Noelle
KFC Genshin Impact set with Noelle stand and Diluc bage
KFC Genshin Impact set with Diluc
KFC Genshin Impact set with Diluc stand and Noelle bage
Link for all sets and singles: https://ali.ski/3GV0K
KFC Genshin Impact Noelle acrylic stand
KFC Genshin Impact Diluc acrylic stand