Spawnsire can only cast what is on your SB. Which means only 4 copies of skittering invasion. Eye of Ugin would be good to tutor spawnsire. Any of the other eldrazi other than Emrakul would work also...Ulamog, Kozilek, pathrazer, etc.

Seeing that this is listed as casual, first comment may not apply. But if truly casual...why not just cast 100 or 1000 skittering invasions and free up space on your MB?

Actually, Pattern of Rebirth is a better tutor for the Spawnsire than the Eye of Ugin, hence me putting it in. As for the amount of Skittering Invasions, 20 of them produce a cool 100 tokens even, which serves as a nice base for the duplication of Parallel Lives.