What is the best size arrows for a 35 pound rucurve (wing archery gull)?

As said above, that all depends on draw length and the weight of the bow at that length. Now, once you have those figures, pick a shaft brand and model you like, head to the manufacturer's website and look around for a spine chart. Different manufacturer produce their charts using different assumptions. If going with Easton, it has been my experience to take whatever the chart tell you and go one spine weaker. So if the chart says to get with group T4, take T3 instead. Other manufacturer, like Carbon Express, seem to be more spot on for me with their assumptions.