[andreasvc]

You could set up a private BitBucket repo and simply give them the link to a .zip download, while you would enter any code you receive into the repo. It might be unfair that you would have to do all the version control, but it's better than nothing...

[stcredzero]

At one company I worked at, we had EVCS. "Eliott Version Control System." Everyone emailed Eliott change sets and he put them together.