The best thing out there for colds is Cold-FX.
It is an extract of ginseng that was developed by a doctor here in Edmonton. It is quite popular in Canada but was blocked in the US by FDA due to lack of accepted randomized controlled trials.
It can be used for prevention taken daily.
Alternatively, it can be used to treat a cold if used very early - kind of similar to acyclovir for cold sores. At the first sign of a cold, I take Cold-FX and the cold's duration is cut in half and its severity is also cut in half.
After my son was born I was constantly getting sick. However, I can't miss many days from work so I had to find a way to get through the illnesses. My colleague had just started using it and found it to be effective. I tried it but haven't really ever been a big fan of herbals and this is still the only one I use (I tried Echinacea in the past but it never worked for me and many studies have come to an inconclusive answer on the question).
I've had great success with it but it hasn't worked quite as well for my wife so YMMV.
I'm not sure if it is available down there. I think it might be but they have to put different labeling on it regarding its efficacy because they didn't satisfy the standard the FDA has for it.