Nothing wrong with grey sets. From my experience, I've never actually had any problems with the lenses I've bought within the first year, be it local warranty or grey. I personally would not hesitate to buy a grey set because I enjoy an upfront savings of the purchase price. Lenses are global products, no difference in quality if bought in the US, HK, Singapore, etc.
That said, having visited some shops recently, I have seen the DA14mm, DA21mm, FA50mm, DA10-17mm fisheye, DA12-24mm, DA16-45mm, DA100mm macro, DA50-200mm available for sale. So if you do some legwork, there are more than enough Pentax lenses to pick up.
This whole lens availability issue to me is an issue blown out of proportion (presumably by overzealous people using other makes who don't want you to consider Pentax). If you can't get what you want in Singapore, one can easily find them online or from other countries (like Malaysia, HK, Japan, US, etc.), and often cheaper than locally. The only issue is whether one is prepared to spend $$$$$ and take the time to look.
The new DA* zoom lenses should already be available. Buy both and most of your shooting needs would be covered. Reality check, how many are willing and able to fork out the money for these beauties? Plus there are the new Carl Zeiss lenses coming soon. So the constraint is always going to be one's budget.
If one's budget is more modest, then give older manual focus lenses a go. I use quite a number of manual lenses that give pretty good results. These are available cheap because far too many photographers are too accustomed to AF that they forget that manual focusing lenses can be just as good. That's the advantage of using a Pentax - backward compatibility.