Is it permissible to commission someone to purchase books at their local price from a bookstore that sells them to foreigners at a double price, and then have this person ship them?

It is permissible to delegate another person to buy books and ship them to you to obtain a better price, unless the seller stipulates a specific condition that you do not meet to qualify for the discount. In that case, it is not permissible for you to delegate another person to benefit from that discount.