Hyalophora cecropia in Denver, CO.

Would there be any way to find them now? Any tips?

Here's an abbreviated quote from "The Wild Silkmoths of N. America":

"Its western limits in the Great Plains are discontinuous; it is common in Nebraska and in the Denver, Colorado area, but not in the mountains to the west. It has been reported from S.Dakota, N.Dakota, Wyoming, & E. Montana. It is uncertain whether the Great Plains populations represent the natural range or are a recent invasion following the westward movement of agriculture across the plains. H. cecropia was not reported in these areas until it became a pest in the late 1920s. Maples, esp. box elder(Acer negunda) were heavily infested, and outbreaks occurred in cycles until the species began a general decline in the late 1940s. It is possible that the records from some areas (e.g., Denver) represent adults inadvertently brought in as cocoons on shrubs & trees shipped from regions where cecropia is native. It is also possible that the moth was always present in low numbers and was simply overlooked before systematic records were kept."

I highly doubt that you can find adults now. This species is univoltine and it flies in the spring. Possibly last instar larvae or cocoons.

I should have specified whatever time you can find the adults, but thanks!