I really have no idea about ordering them from overseas & clearing Singapore customs, especially scopes which are meant for firearm use, for all I know you may need to clarify in person when it arrives that its for photography use. Also the scopes for firearm use cant be mounted to the hot shoe without an adapter.
Just drop in Orient Photo & check them out, they have an open frame design & a tubular design with hot shoe mount. IIRC they are made in the PRC, quite affordable.