It's not that easy to clone something. For example, you can't just go buy a simulclass transformer (except from Mesa). It's got a somewhat unique way of being wound. So, while there are lots of output transformers that are built for tube amps (Hammond et al), there isn't one off-the-shelf that mimics the ones used for a simulclass amp. You could ask for a custom run of transformers wound to the simulclass specs, but I think that it usually only makes sense for a minimum buy of something like 500. That's out of reach for a hobby-level C+ clone project.
There are C+ clones out there. You can check out the folks at SLO Clone...that's where I've seen people doing C+ clones. They almost always just do the pre-amp, though. And, while you might think that the pre-amp might capture the essence of the C+, you'd find that you'd be wrong. The sound of any quality amp (not just the C+) finds itself being affected by all parts of the amp...pre-amp, power-amp, cab, and speaker...in startling ways.
I myself am a C+ owner (well, a IIC to IIC+ factory upgrade actually) and I'm also an amp modder/tweaker. I myself built a IIC+ pre-amp based on the schematics on the web (later confirmed with my own IIC+). I then grafted it into a Fender Deluxe Reverb Reissue...which is a nice little tube amp. It sounded horrible. Totally wrong. Sure, the circuit was correct compared to the schematic...but the schematic doesn't make the sound, the whole amp does. Just connecting the right value resistors and capacitors in the right order does not give you the right sound. That's what this exercise taught me. It taught me that you've got to get the physical layout of the circuit board to be the same, the length of wiring from the pots to the PCB to the tubes all has to be similar (my amp probably had 2-3x the length of internal wiring), the DC voltages need to be similar (the Fender power xformer output is about 100-150V lower), and then the voicing of the power amp, presence (which is a power amp function, not a pre-amp function), cabinet, and speaker all need to be similar. It's stunning what contributes to the sound *and feel* of a good amp. My FrankenFender was not it.
So, if someone wants to try to clone....that would be awesome. I don't think that they'll ever get close...not because of some magical Mark IIC+ pixie dust...but because it's hard to copy the sound of *any* amp convincingly. There are just too many variables. Frankly, unless Mesa literally copied there own circuit board patterns (which are a tangled mess in my IIC+), and magically got the right caps and right transformers made, and got their old wiring lady out of retirement (if she'd still put up with that nasty tight wiring job inside the IIC+), and got EVM to make the 12-L speaker to *really* sound like the original one....well, i don't even think that Mesa could make a clone of their own IIC+.
To each, there is its time. Then its time passes. So, let's all go buy an Electodyne or a Royal Atlantic...maybe one of those will be the next classic that everyone will be longing for in 25 years.
Chip