I have seen plenty of yellow with royal blue polyps. They are quite common now. Try Reefer Madness frag section or monty's hand picked. If I am not mistaken they are Montipora Peltiformis, but to be honest you can only be sure if your an expert like Eric B. and you feel like killing it to study it. They have some nice size ones for around $120 from time to time. I have also seen lots of frags about 1-2" for around $60 on some other web sites. To much for a frag IMO. Reefer Madness has or had them for around $25. Hope this helps....
Abran