you have some good ideas for a shrieker counter here.
sundials - perfect
oty - creature control on a stick, but needs a buff to eat a shrieker
RoF - nice,
if graboids/shriekers are unburrowed
dim shield - stops shriekers completly
but i seems you demand a bit too much for that "little" (32 cards) rainbow.
for building a good working rainbow: 9 Tips for Better Deck Building #8 (
http://elementscommunity.org/forum/index.php/topic,3329.0.html)
maybe a dou deck (time/aether?) is more sucessfull to stop a shrieker rush