What should we do with meat gifted to us by a non-Muslim father, knowing that its source is doubtful, and we cannot determine a specific place to buy halal meat?

Firstly: Supplicate for your father's guidance and exert effort in inviting him [to Islam] in cooperation with your husband.

Secondly: Regarding eating meat in the lands of the disbelievers, one can refer to answer number (24019).

Thirdly: You can inform the man, in a gentle and suggestive manner, about the place where halal (definition) meat can be purchased, explaining the Shariah-compliant and health reasons, without imposing it. You should also praise his generosity and clarify your eagerness to avoid any embarrassment. It is expected that a generous person would accept this.