The company we insured with was a UK company called William Russell (address follows) which specialises in 'expat' insurance. They don't care where you are resident. Premiums are not cheap, but there are different levels of coverage, and if you stay out of North America, the premiums are about half as much for the rest of the world.
Haven't heard of IMG, but there are definitely other UK companies who provide medical insurance.
As for bike insurance, I'm afraid you're out of luck. Get a good lock and alarm system, and use a cover on the bike overnight, is the best advice we can give. Ironically, if the bike is large or unusual, it's safer from theft in the 3rd world than in Europe or N. America.
William Russell Limited
Suite 201, The Mayford Centre,
Smarts Heath Road
Woking Surrey GU22 0PP
Tel: +44 (0)1483 - 799 844
Fax: +44 (0)1483 - 799 855