Hi Davit
open.sap.com will offer a HCP extensions course soon - and there will be a week of C4C extensions. That will provide a tenant, but only for the week of the course.
Unfortunately you do need to be part of our partner program. I'd suggest you reach out directly to falk.pichl@sap.com or sri.rajagopalan@sap.com - these are the guys I forwarded your question to.
Regards
Ginger