Has anyone been to any of the F1 GP's abroad before? If so how did you go about sourcing tickets from a reliable source?

It's looking I may be in Singapore in September when the F1 is on and would love to go and watch it, i'm hoping that I can get into our offices to watch from high up(in Marina Bay) but weighing up my options. I've googled it and loads of sites come up but unsure as to what ones are genuine...

Cheers