For political issues, you should petition governments directly on issues.
Not sure if this is a great alternative. This is a thing that is totally dependent from country to country. In my country, there is no such platform that I'm aware of (on the local or national level at least. Ok, I may petition the EU, but they may just have no responsibility into my matters).
Many institutions do have email addresses though, and if, for example, you have a website, you can write an email template and point to an institution where people could send that email. Even that I don't know how feasible it could be, but it could be more doable in more parts of the world, I think.
Otherwise, for Romania there is declic.ro, a platform owned by an NGO who relies solely on donations to run it, and also runs its own campaigns.