If a Jew is entertaining non-Jews in a business setting is he allowed to buy them non-kosher food in a non-kosher restaurant?
from Dose of Halacha:
The Shulchan Aruch (YD 117:1) writes that one mustn’t do business with any food which is forbidden to eat mideoraisa. The Rema and Beis Yosef (YD 117) write that one mustn’t, therefore, buy such food for one’s non-Jewish workers as one stands to benefit from giving such gifts (See Kaf Hachaim YD 117:28).
The Taz (YD 117:2), however, allows buying such food for workers, as this does not constitute business (See Shach YD 117:3).
He continues to explain that this doesn't apply to everything, as one can't for example, buy anything that is made up of meat and milk, etc:
As meat and milk that were cooked together are assur behanaah, (forbidden to benefit from, See Shulchan Aruch YD 87:1), if one received such a food product, one may not even pass it on to a non-Jew. The Rema writes that this doesn’t apply to chicken cooked in milk (or other foods assur miderabanan). Thus, one may buy food that is bishul akum, etc.
The Kaf Hachaim (YD 117:52) writes, however, that even those poskim who are stringent would allow buying gifts for non-Jews. Likewise, the Aruch Hashulchan (YD 117:19) writes that one doesn’t need to spend more money in order to buy Kosher food.