I bought an udhiya (sacrificial animal) and then found out that it had a defect. Therefore, I sold it and spent its price without giving out from it in charity. What is the ruling [for this] in Islamic law?

According to the opinion implemented for fatwa, which is the opinion of the majority of scholars, the udhiya is a confirmed Sunnah and not an obligation.
Based on this, you are not blameworthy provided you did not vow to offer an udhiya. Otherwise, you must buy another animal and slaughter it in place of the one you sold.

Allah Almighty knows best.