The basic principle is that it is permissible for Muslims to buy whatever they need of the things that Allah has permitted whether from a Muslim or a Kafir. The Prophet (peace be upon him) bought from the Jews. But if a Muslim refrains from buying from fellow Muslims for no good reason - such as due to cheating, high prices, or having low quality products - and they would rather buy from a Kafir, and they prefer them, with no reason, this is Haram, because it implies their aligning themselves with the Kafirs, approving of them and liking them. On the other hand, they will be causing losses to Muslim traders, a recession in their trade, and non-marketability of their products if Muslims take that as a habit. But if there are reasons behind refraining to buy, such as those mentioned previously, then they should advise their Muslim trading brothers to remedy these faults that cause them to turn away from dealing with them. If they accept the advice, Al-Hamdu li-Allah (All praise be to Allah), otherwise it is permissible to turn to other traders, even if they are Kafirs, as long as they exchange benefits properly and are honest in their transactions. (Part No. 13; Page No. 19)
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.