Your best bet will probably be a Cyclops. These come in a range of sizes and can be mounted above or below an A-frame.
They don't appear to have a web site yet, but one of their American distributors has and it's probably worth a look: http://www.jasco.com/cyclops.html
Cyclops Technologies Ltd
PO Box 6
Phone: 01243 841123
Fax: 01243 829321