does anybody know where i can buy pentax lenses and should i buy in BKK or Singapore ?

what about this lens 55-300mm is it good for animal/nature shoots for longer distance,or is there better alternative?

A fast look through online stores and Craigslist gives the nod to Singapore. I've never found Thailand to be a great place for buying electronics or cameras.

Craigslist is the definitive scammers list, as most people in the know- know, so I'd avoid/ignore this at all costs.

The 55-200 is a very soft (read crap) lens. You will be disappointed!

In real terms anything above 3x zoom is a severe compromise on quality - re-adjust your thinking for IQ.

What camera are you using?

Cropped/FF?

This is more significant than cost.

k7 with kitlens 18-55

My immediate thought was Fotofile but suprisingly they do not mention Pentax.

Only generics like Sigma so Singapore may be your best bet.

However do checkout DPreview to see what lenses are recommended before buying.

Even there the Pentax offerings are very limited.