Please disregard my earlier comment. It isn't mineral oil that came recommended, it was wintergreen oil. I really should have gone back to find the link the first time. Apologies, I'm always jumping around in different corners of the web, and when a neat thing "sticks" with me, sometimes it doesn't stick quite correctly.
From Kevin Kelly's "Cool Tools" website:
Wintergreen oil (methyl salicylate) is the most penetrating of all penetrating oils. It is available at most drugstores at minimal cost. If you work on old machinery that is anywhere near saltwater (or salted highways) it's an essential weapon in tackling otherwise hopelessly rusted/frozen threads. It smells good, and though toxic and not to be kept within reach of children, is intended for topical application to human skin.
-- George Dyson
Another possibility for you: "Rust Buster"
"As a DIY'er, this is one of my favorite products because it REALLY works. I came across it by accident at a small tractor supply store in southern Missouri. The product typically works instantly, but on heavy duty applications, I like to apply a little (or a lot) on a rusted or frozen bolt or car part, tap the part lightly to aid penetration, and wait. After a few minutes, rusted bolts, screws, shafts, piping, any types of "frozen" connections and assemblies will now break lose. I have tried a variety of other loosening products, but they tend to use heavier oils that don't penetrate as well. Smaller hardware stores, and farm supply stores will probably stock it.
-- Mike Farley
Zoom Spout Rust Buster
Rust-Buster may not necessarily be available over there, but with the extreme humidity, any farm-equipment operators may have something similar.
Added: Kano Kroil gets a lot of positive feedback.
With any of these solutions, you'll have better luck if you take your time; multiple applications over the course of a week or more. Also, tap the parts with a hammer which will aid in separating the rusted surfaces and allow the oil to penetrate further. Even better, apply a regular vibration to it. If you're an audiophile, strap a transducer to the bike frame. Or, spread a blanket on top of a clothes dryer, then strap the bike down on top and feed Bahts into it for a few hours.