One challenge we have is actually getting dedicated research time scheduled in with our clients - account managers own the relationship and have other priorities when getting clients on a call. How do you overcome this barrier to make sure product marketers are able to ask the questions they need to learn from clients?

Position it as a VIP sneak preview to talk to clients. Share that you want clients’ input to help inform / influence the roadmap.

Create a Beta and / or Customer Advisory Board (CAB): Formally establish a beta or CAB, a group of customers that opt into providing input. Again you can position this as a VIP group that gets early access to new features, sneak preview of the roadmap, etc. Make this group exclusive, where account managers have to apply to get their customers accepted. With these groups, always ensure they are diverse and reflective of your ICP, though it can shift based on your goals. 

Develop strong relationships with sales, by identifying a handful of key sales folks that you want to build relationships with and invest in helping them, and in return they will help you.