In he case of Tillicum, if it is privately owned, you must either purchase it, get someone sympathetic to your cause to purchase it, or approach the current owner with your ideas and get them to agree to go along with it.
If you can work that out, get some like minded individuals together, (5 or more) and come up with a name for your group. Do a name search through the BC business registry to be sure you can use the name. If so, fill out the documents to create a non profit organization and send them off. If one of the folks in your group is the land owner, even better.
Approach the local politicians with your ideas and find someone there that will champion your cause.
If you can have the site recognized as one of heritage value, which it is, then you can begin attracting interest in it from many sources. Start cleaning it up and having events there. List it as a destination in the community for tourism.
Hope this helps.