For content that's already out, you need to identify who the influencers are who'll share your content to the people you want to reach?
e.g. do you have a list of GC people with big social media followings across all platforms?
Do you know who they are? Do some research, make a list.
Then, for those who you know are onside, contact them privately and ask for help sharing your content.
For new content, contact sympathetic national press contacts first, let them know you've got something coming up and ask if they're interested in covering it.
Get someone to write a really good press release. If at all possible, don't have someone amateur do it. Get someone with good writing skills and decent PR experience to write it. I've seen so many bad press releases sent out by various campaigns (in different fields) over the years, and it's such a shame as they just get ignored by journos. There's a format for press releases that needs to be followed. It's not hard, but if people don't know about it, they won't do it.
Contact the influencers ahead of time also and let them know to expect it.