Personally I used Zythos in mine since I couldn't get Sorachi. How I wound up at this substitute I don't really recall, I'm still a brewing newbie. But I can say this, the brew turned out amazing. Everyone I have shard it with has loved it and I've forwarded the recipe to two other home brewers..
Brewed this (slight variations to citrus based on what was available) as my first all grain batch, opened bottles last weekend and it is incredible! Great recipe!!