At www.hlj.com
They said that the 1/60 Big Scale Strike Gundam Striker packs are not compatible with 1/60 PG Strike. It is mentioned when you look up the 1/60 PG Strike.
That's where I normally go. There and also Hobby search.
Good deals and shipping... items usually in stock.

http://www.hlj.com
http://www.1999.co.jp/eng/