Between the 17th of Tammuz and Tisha B'av
10. During the nine days [between Rosh Chodesh Av and Tish'ah B'av], one should not make (or have made) new clothes or new shoes, nor should one weave new socks (1). [These restrictions apply] even when these tasks are performed by a Gentile (2). In a case of great necessity, for example, when a person is getting married directly after Tish'ah B'av [and needs new clothing], it is permitted to have a Gentile carry out the task, but not a Jew (3). Before Rosh Chodesh Av, it is permitted to commission a Jewish tailor [to make clothing], and, in that circumstance, he is permitted to make them even during the nine days (4).
(1) One is not even allowed to wear any new clothing for the first time during the nine days (Shulchan Aruch 551:6). This prohibition includes wearing new shoes, shirts, socks and underwear ("Summary of the Halachos of the Three Weeks," by Rav Shimon Eider, pg 11). Similarly, one may not purchase new garments or shoes during the nine days, even if one does not intend to wear them until after Tish'ah B'av (Mishna Berura 551:49).
The reason for these prohibitions is that there is an element of joy in wearing, making and purchasing new clothing.
(2) According to the Rama (551:7), it was common for people in his time to commission a Gentile during the nine days to make new clothing to be picked up after Tish'ah B'av; however, he writes that it is best to avoid doing so ("Tov Lema'et Ba'zeh") wherever possible.
(3) The Mishna Berura (Ibid.46) permits even a Jew to make clothes for the bride and groom.
(4) A Jewish tailor who is poor and needs to make and sell clothing in order to have enough money to buy food, may do so during the nine days. Furthermore, if it is clear to all that the clothes he is making are for a Gentile, it is permissible for the Jewish tailor to make them during the nine days, even if he is not poor (Ibid. 52).