Q: Is there a way to move iTunes purchases from a gmail account to an existing iCloud account?

Hi, len64.  

Thank you for visiting Apple Support Communities.  

I understand that you want to move media purchased with one Apple ID to another.  At this time you cannot merge Apple ID accounts.  Any purchases made with an Apple ID are linked the original account that was used to purchase this media.  

Can I merge multiple Apple IDs into one?

Apple IDs can't be merged. We recommend that you use the same Apple ID in the iTunes Store and iCloud. Using multiple Apple IDs might be confusing and might cause issues with accessing purchased content or using some services. 

If you need more than one Apple ID, you can still access your purchased items (such as music, movies, or software) using your other Apple IDs. Learn how to use multiple Apple IDs with iTunes and iCloud.

Frequently asked questions about Apple ID

However, Family Sharing may be a solution as it sounds like you already have two existing Apple ID or iCloud accounts.  Take a look at the article below as it provides more information on this feature.  

Family Sharing

Set up Family Sharing

Cheers