How To Recover All Deleted Local Files Which Were Deleted Using Command (Git Checkout ...)?

I had a project which I wanted to push to Git. So I create a local repo (git init). I had a .gitignore in remote repo so I couldn't push my local files to remote. So I did git checkout origin/master, and all my local files are gone.

Is there any way to recover them?

Here's what I have done:

git init
git add .
git commit -m "Initial commit"
git push origin master (failed)
git checkout origin/master

Assuming your git commit -m "Initial commit" step actually completed successfully, then your local master should have all your work. You may switch to that branch to verify this:

git checkout master

I don't know why you thought to checkout origin/master. This is the remote tracking branch, and it doesn't really have anything to do with your current problem. You need to resolve the reason why your pushes are being rejected.