Seems a little odd that you'd get into game development without having at least a few ideas ticking away at the back of your head. Maybe you need to exercise your creativity rather than just mooch ideas from other people.
Some ways you could do this:
- Watch gameplay videos of games you enjoy, and write down elements of the gameplay that you find particularly interesting or you think would be interesting to attempt to replicate yourself. For example, Mega Man features bosses whose powers can be used once they've been defeated; how would you build a game around that premise?
- Find a relatively simple game, like Pac-Man for example, and try to find ways to expand on their basic gameplay mechanisms, or even improve on their current ones. Pac-Man could get temporary boosts, persistent upgrades, new abilities, etc.
- Read reviews of games that point out particular flaws in those games, then see if you can create an isolated example of fixing those flaws. For example, the stealth mechanisms in Assassin's Creed are often seen as "cheap" - how would you go about making a stealth game that forces players to be more mindful of their actions and environment?
This isn't meant to be a way to simply copycat other games and mechanics, but once you start training your brain to see games critically - and more importantly, think of ways how you would do better - you'll find that the ideas start to flow. Unlocking creative thinking is a vital part of mastering anything.