You need to target seed stage investors who like to "follow." Your current investors act as validation for your idea and deal. Investment is a game of knocking on the right doors versus sales, which is just knocking on a lot of doors. Ask around your network for investors that have done similar deals in the past to what you are proposing. Connect with them and gauge their interest and what they'd be able to bring to the table. Keep up meetings and provide updates, getting them excited about what you're up to. Presenting at a game-centric Angel Forum is another avenue.

You literally have done the "hard" part, you have a lead investor. You've made it where 99% of venture-backed businesses don't. However, getting people to part with large sums of money still takes time, they need to trust you will do well with it. Keep talking to seed stage investors who have funded ideas like yours and you'll get there.