OpenSSH anything like 'internal-sftp' but for SCP?

Take a look at rssh which is an alternative shell that allows limited access to a system.

rssh is a restricted shell for providing limited access to a host via ssh(1), allowing a user whose shell is configured to rssh to use one or more of the command(s) scp(1), sftp(1) cvs(1), rdist(1), and rsync(1), and only those commands.

You can configure which commands can be used on a per-user or system wide basis using the rssh.conf file

Alternatively you can use scponly to do what you want. It acts as a wrapper to the ssh suite and allows file transfer but not shell access.

Do you need to do this through ssh?

IF so you can try setting their shell to:

/usr/libexec/openssh/sftp-server

And make sure you add the above into /etc/shells

If you want to decouple from using built in accounts, you can setup proftpd

I setup a secure SFTP using proftpd. compiled proftpd like so:

./configure --prefix=/usr --sysconfdir=/etc --with-modules=mod_sftp

Can use this article below, and some more on google on how to set it up:

http://tutorialgenius.blogspot.com/2012/02/linux-installing-and-configuring.html