Shiro Sword

Does anyone know where or how I can get a Shiro sword?

By defeating him and trading the Amulet of the Mists in Divine Path.
Only one amulet per character.
Although i wouldn't know why sicne the req is waaaaay too high.

It has a requirement of 15 swordmanship or something stupid.

Do better buying the Katana from the weapons guy after you defeat Shiro as it comes with a +5 energy already built in and only requires 9 swordmanship. Then add a vampiric mod and a health bonus onto it.

It'll cost a bit but be a much better sword (imo)

May i suggest you look at Victos blade... Same stats except the req is 9 and not 15... Has a way cooler skin to imo.

No, it's a much worse sword if you actually plan to use it for fighting, as Energy +5 does little compared to any Damage +15% modifier. 15 Swordsmanship isn't that particularly hard to get for a warrior, really. But it'd actually be a lot cheaper to buy a Victo's Blade, which has the same stats as Shiro's except with a requirement of 9 and a price of less than 5k usually.

Where can i buy a Victos sword?

At your local retailer in Lions Arch, Kamadan, Kaineng, Droknar's Forge. Just spam WTB Victo's Blade 5k

Or you can look at GWG's auction site to see if someone is auctioning a Victo's Blade:

http://www.guildwarsguru.com/auction/

Or you can check out the Ventari's Sell forums to either post in the "buy" forum or see if someone is selling it in the "Sell" forum:

http://www.guildwarsguru.com/forum/forumdisplay.php?f=6