Disclaimer: I haven't tried any of these out, but they appear to be what OP is looking for. These links were just from looking through some Google Code Search results.
I found a C# version. The project doesn't have any frills; it's just the source. However, it appears to be doing the algorithm just from my first cursory scan. In particular, you will want to look at this file.
For C++, I found some code in this google code project. The code is, of course, in English, but the wiki is all in a Cyrillic-written language (Russian?). You will want to look mostly at this file. It appears to have both a serial and and parallel version of Strassen's algorithm.
These projects may not be fully correct, but they are things at which you might want to look more closely.