ck4707, I couldn't get your link to work.
Here's
another link to Misco. I couldn't find the unit you refer to either, but here's one they do for £37.99:
DYNAMODE RJ45 - BNC MEDIA CONVERTER
Link Misco No.: 41503
This 10Mbps RJ45 to BNC converter is a media converter that converts 10BaseT Ethernet UTP medium to the thin Ethernet coaxial medium, and vice versa. The 10Mbps RJ45 to BNC converter provides one UTP/STP port for connection to a UTP/STP cable segment. This media converter provides a low-cost and extremely easy to install solution to a mixed media environment.
It is especially useful in connecting a small departmental workgroup to main 10BaseT network.
General
Height 1.8 cm
Depth 8 cm
Width 4.4 cm
Enclosure Color Grey
Enclosure Type External
Device Type Repeater
Weight 85 g
Networking
Max Transfer Distance 185 m
Status Indicators Link activity, collision status, power
Data Link Protocol Ethernet
Connectivity Technology Cable - 10Base-T, 10Base-2 (coax)
Data Transfer Rate 10 Mbps
Compliant Standards IEEE 802.3-LAN