Is it permissible for the buyer, after writing a Salam contract and before the delivery date, to judicially demand the imposition of a penalty clause on the seller to ensure his commitment to the delivery date, especially since the seller refuses this and currently does not possess the means to return the money to the buyer?

This type of penalty clause is impermissible, as it constitutes an affirmation of a delay in debt repayment. It is not permissible to stipulate the payment of a sum upon delayed payment, as this is usury (riba). Therefore, you are not allowed to stip stipulate this penalty clause, nor do you have the right to bring the matter before a judge concerning it. Any condition stipulated after the time of the contract is not binding on the other party. If the time for delivery arrives and he delays delivering the commodity out of procrastination, then you may refer his case to a judge. However, if he is in financial difficulty, he must be given respite, as Allah Almighty says: "And if there is one in [financial] hardship, then [let there be] a delay until [a time of] ease."