Hello, I don't know of free Renko source code but if you are new to Renko that is probably not the place to begin.
You might check out the work of Sergey Deev (work4it) who has developed a UniversalEA and Renko indicators that work together to form a functioning ONLINE Renko EA. I am trading some of them now for forward testing. I suggest you use a DEMO and not alive account. So far the results are interesting but not overall profitable (the test is only running about a week.) He sells the EA and indicators that form the ONLINE working EA with a variety of strategies. Check it out and consider the pros and cons before risking real money.
I have posted more about these on my profile page and will keep it going after the new year. This is my holiday break from active trading.