Update***
The TSD M4's we see here are indeed from SRC it has been confirmed from BuyAirsoft.ca, here's the email response I got:
Hello,
We have just been informed from TSD that these guns are OEM by SRC. TSD have teamed up with SRC ( not JBU as stated on the website), to completely re-do their what was previously a “Crappy” AEG, into a MUCH better performing one, competing with the other top end brands. SRC confronted TSD and asked for their help to get this new gun re-designed. TSD was able to let them know what was “crappy” about their previous guns, and have these features changed to create the new “’07 TSD Tacticals”. These guns have been going over very well in the states for being a very well priced full metal AEG that stands up to the other top end brands. I hope this information helps you out a little. We are now in the process of updating our website to include this information, and to clear the air up about them being TSD/JBU guns. Below is a link with some great close up pictures of these guns. Enjoy!
http://www.wgcshop.com/pcart/shopper.php?cat=SRC%20AEGs