Is it permissible to pay a commission or offer a gift/sum of money to friends who work in companies in exchange for informing me about tenders and projects, knowing that the decision to award the project is not within their authority?

There is no objection to agreeing with individuals who work in companies to receive a commission in exchange for informing them about the existence of tenders or projects within their companies, unless this is part of their official duties, or it results in harm to the companies, or it causes them to miss out on benefits. If it does result in harm, then it is not permissible. If it is permissible to give them the agreed-upon commission, then it is also permissible to give them a gift or a sum of money without a prior agreement.