You can get it from the BSI online website if you or your company are a subscriber that is. If not I think you can buy it online.
http://www.bsi-global.com
Please note that there are several standards relating to ROV interfaces and also there are several interfaces that are not in the standards. For example there are various designs of hotstabs that do not match the standards.
API 17H is a direct copy of BS ISO 13628-8 word for word so if you have access to the API website then you can get it from there as well.
http://www.api.org or http://www.ihs.com
If you are looking specifically for torque tool interfaces please bear in mind that between the two API standards 17D & 17H (identical to ISO 13628-8 ) some of the interfaces are the same. For Example Class 1-5 Rotary Docking interface is the same, but Class 6-7 Rotary Docking interfaces are different. Also the Rotary High Torque interface is only in the ISO 13628-8 and the API 17H.
API 17D is the original American Spec for ROV interfaces and was the first one to be issued.
There is also BS ISO 13628 – 9 for Remotely Operated Tools which covers guide wire deployed tools, tie in tools, etc
If you are in Brazil Petrobras have their own set of standards for ROV interfaces some of which bear no relation to the the API or ISO standards. For example Rotary Torque Tool interface has slots in the receptacle like the Class 1-7 Rotary docking interface but the receptacle diameter is similar to the Rotary High Torque Interface so it is a combination of both interfaces from the ISO & API standards.