Is it permissible to expiate for breaking an oath by distributing clothing to the poor that does not fully cover the body, and if ten poor people are not available for feeding, is it obligatory to provide ten complete sets of clothing or is it sufficient to provide ten different pieces?

If you wish to atone for your oath, you have the choice between feeding ten poor persons, clothing them, or freeing a slave. If you are unable to do these three, then you must fast for three consecutive days. The sufficient clothing is that which covers the 'awrah for prayer. Some scholars have gone to say that what is customarily considered normal clothing is sufficient. What you mentioned about giving out clothes that do not cover the 'awrah is not sufficient if they do not cover a man's 'awrah in front of men, or a woman's 'awrah in front of women. As for the claim that there are no poor persons, this is difficult to imagine in Muslim countries.