Buying a New Phone

You can buy the iPhone Xs, Xs Max or Xr from any Apple Re-seller in Sri Lanka.

See here for locations: Apple Authorized Re-seller locations in Colombo,Sri Lanka - Apple support

As mentioned, Apple no longer sells the regular iPhone X. Some re-sellers may however have left over stock.

Apple no longer sells the X.

You can't buy the iPhone X directly at Apple anymore. Look for other shops that sell third-party.

Click the link provided above for authorized re-sellers in Colombo, Sri Lanka.