Google Summer Of Code

I can't mentor you aa I haven't cleared GSOC myself. I will be trying again this year. But the advice I can give you is this -
Take a look at previous year's organizations, and identify some to whom you'll like to contribute and have the required skills. Once you identify such organizations, join the organizations communication channel - Slack/IRC/Mattermost etc and ask for mentorship there too.
In the end, the organization is going to decide who to select and recently the competition has grown so much that you need to have atleast a couple of merged PRs to even be considered.