Ok, a rather simple question.

Can a character with Missile Parry adept power and a weapon foci (Sword) use the blade to parry them with – do they gain the benefit of Reach.

In this case it would be Reach+Reaction+Power

Sounds rather reasonable as long as they don’t want to keep the arrows/daggers/other but just swat them out of the air.

Still, that would also mean that Trolls would be able to use natural reach.

I would say 'no' to reach. The reach bonus comes from the advantage gained in the back-and-forth abstractness of SR melee combat. In this case, that aspect just isn't there.
Also, it isn't using the unarmed or blades skill, it's reaction.
Your point about Trolls is really the clincher for me.

look at it this way...
GM: bad guy A shoots at you - he's further away so he's going to use his reach bonus to apply a negative modifier on your missile parry....
Player: but...but....

Has anybody ever used missile parry ?
Nobody uses projectile weapons, and IF somebody uses them, its runners, not guards . . .

In Britain as i run plenty of people use Projectiles as the gun laws are strict...

Where did that thread go about the 15D damage bow?

I don't know the answer to your question, Jopp, but I can share my experience.

I have had experience trying to block or parry arrows (like this) with a sword, shield, long (bastard) sword, and polearm. The shield is the easiest (natch). The rest of them are about the same. The only real difference that I've found in parrying arrows with weapons of differing length is when exactly you need to move them to intercept the arrow. The longer weapons don't really give one that much extra time to block a fast-moving object.

Consider: is it easier to hit a ball with a tennis racket than it is with a racquetball racket?