You can use a BNC-BNC coaxial cable, a male BNC T-piece on the oscilloscope side connected to the scope, and a terminator on the other side of the T-piece.
(Sometimes I get a bit annoyed when I want a 50 ohm BNC patch lead, a tee or a terminator and I can't find one, but years ago when everyone replaced their 10-base coax LANs there must have been millions of the thing tossed in the trash.)