There are tons on Amazon, including Prime versions with free shipping and returns:
Capezio Women's Long Sleeve Unitard,Black,Small https://www.amazon.com/dp/B000NM06K4/ref=cm_sw_r_cp_api_i_pzb8Db4T8SW9W
Eurotard 10129 Womens Long Sleeve Unitard (Medium,Black) https://www.amazon.com/dp/B003NZMSGS/ref=cm_sw_r_cp_api_i_Wzb8DbB25FJDN
OVIGILY Women's Long Sleeve Unitard Dance Costume Spandex Full Body Suits https://www.amazon.com/dp/B07TYYRQDL/ref=cm_sw_r_cp_api_i_uyb8DbFVGCN4G
Speerise Adult High Neck Zip One Piece Unitard Full Body Leotard, M, Black https://www.amazon.com/dp/B01I38X4JE/ref=cm_sw_r_cp_api_i_-yb8DbE28HBWB