I work on a small team of devs, 4 guys.  They have all used source control.  Most of them can't stand source control and instead choose not to use it. I strongly believe source control is a necessary part of professional development. Several issues make it very difficult to convince them to use source control:


The team is not used to using TFS.  I've had 2 training sessions, but was only allotted 1 hour which is insufficient.
Team members directly modify code on the
server.  This keeps code out of sync.  Requiring comparison just to be sure you are working with the latest code.  And complex merge problems arise
Time estimates offered by developers exclude time required to fix any of these problems.  So, if I say nono it will take 10x longer...I have to constantly explain these issues and risk myself because now management may perceive me as "slow".
The physical files on the server differ in unknown ways over ~100 files.  Merging requires knowledge of the project at hand and, therefore, developer cooperation which I am not able to obtain.
Other projects are falling out of sync.  Developers continue to have a distrust of source control and therefore compound the issue by not using source control.
Developers argue that using source control is wasteful because merging is error prone and difficult.  This is a difficult point to argue, because when source control is being so badly mis-used and source control continually bypassed, it is error prone indeed.  Therefore, the evidence "speaks for itself" in their view.
Developers argue that directly modifying server code, bypassing TFS saves time.  This is also difficult to argue.  Because the merge required to synchronize the code to start with is time consuming.  Multiply this by the 10+ projects we manage.  
Permanent files are often stored in the same directory as the web project.  So publishing (full publish) erases these files that are not in source control.  This also drives distrust for source control.  Because "publishing breaks the project".  Fixing this (moving stored files out of the solution subfolders) takes a great deal of time and debugging as these locations are not set in web.config and often exist across multiple code points.


So, the culture persists itself.  Bad practice begets more bad practice.  Bad solutions drive new hacks to "fix" much deeper, much more time consuming problems.  Servers, hard drive space are extremely difficult to come by.  Yet, user expectations are rising.

What can be done in this situation?

It's not a training issue, it's a human factors issue. They do not want to, and are creating road blocks. Deal with the broken group dynamics, what is the root cause of their objection - usually fear, is it just fear of change, or is it more sinister.  

No professional developer today, or for the last 20 years, has resisted source control. Once, about 30 or 40 years ago, when computers were slow, source control even slower and programs consisted of one 500 line file, it was a pain and there were valid reasons not to use it. These objections can only be coming from the worst kind of cowboys I can think of.

Is the system forced on them making their lives difficult in some way?  Find out what it is, and change the system to invalidate the objection. Repeat until done. 

I suggest looking at GIT or Mercurial. You can create a repository in each source code tree, they won't even notice and can keep on hacking the way they do now. You can track the changes they have hacked into the code base, make commits, merge them into other source trees etc. When they see you do a merge of a weeks worth of effort into another product in seconds, they might change their ideas. When you roll back one of their screw ups with one command, and save their ass, they might even thank you (don't count on it). At worst, you look good in front of the boss and, for a bonus, make them look like the cowboys they are. 


  Merging would take not only a great knowledge of the project


In that case, I am afraid you're up the proverbial creek with no paddle. If merging is not an option, neither is implementing it, so you are saying that you can no longer add features you already have in one branch (term used loosely) to another. 

If I were you I would reconsider my career prospects...
